以下是我使用bootstrap-table渲染表格，但是表格表头不固定，应该怎么修改，谢谢

$('#tb_modu').bootstrapTable({
            url: '/Module/get_modu',            //请求后台的URL（*）
            method: 'get',                      //请求方式（*）
            toolbar:"#tlb_modu",
            cache: false,                       //是否使用缓存，默认为true，所以一般情况下需要设置一下这个属性（*）
            pagination: true,                   //是否显示分页（*）
            sortable: true,                     //是否启用排序
            sortOrder: "asc",                   //排序方式 从小到大
            queryParams: function (params) {
                var temp = {   //这里的键的名字和控制器的变量名必须一直，这边改动，控制器也需要改成一样的
                    limit: params.limit,   //页面大小
                    offset: params.offset,  //页码
                    search: '{"modu_code":"' + params.search + '","modu_name":"' + params.search + '","modu_state":"' + $('#conditions').val() + '"}'
                };
                return temp;
            },//传递参数（*）
            sidePagination: "server",           //分页方式：client客户端分页，server服务端分页（*）
            pageNumber: 1,                       //初始化加载第一页，默认第一页
            pageSize: 100,                       //每页的记录行数（*）
            pageList: [100, 150, 250, 500],        //可供选择的每页的行数（*）
            search: true,                       //是否显示表格搜索，此搜索是客户端搜索，不会进服务端，所以，个人感觉意义不大
            showColumns: true,                  //是否显示所有的列
            showRefresh: true,                  //是否显示刷新按钮
            minimumCountColumns: 2,             //最少允许的列数
            clickToSelect: true,                //是否启用点击选中行
            height: $('.modu').height(),
            uniqueId: 'modu_id',                //每一行的唯一标识，一般为主键列
            showToggle: false,                   //是否显示详细视图和列表视图的切换按钮
            cardView: false,                    //是否显示详细视图
            detailView: false,                   //是否显示父子表
            searchOnEnterKey: true,
            showExport: true,                   //显示导出按钮 
            exportDataType: 'all',              //导出类型  
            treeShowField: 'modu_name',
            idField: 'modu_id',
            parentIdField: 'modu_modu_id',
            singleSelect: true,
            onLoadSuccess: function (data) {
                
            },
            columns: [{
                checkbox: true
            }, {
                field: 'modu_id',
                title: '模块id',
                visible: false,
                formatter: function (value, row, index) {
                    if (row.disable_time != null) {
                        var a = '<span style="color:red;">' + value + '</span>';
                    } else {
                        var a = '<span>' + value + '</span>';
                    }
                    return a;
                },
            }, {
                field: 'modu_modu_id',
                title: '上级模块id',
                visible: false,
                formatter: function (value, row, index) {
                    if (row.disable_time != null) {
                        var a = '<span style="color:red;">' + value + '</span>';
                    } else {
                        var a = '<span>' + value + '</span>';
                    }
                    return a;
                },
            }, {
                field: 'modu_code',
                title: '模块编码',
                formatter: function (value, row, index) {
                    if (row.disable_time != null) {
                        var a = '<span style="color:red;">' + value + '</span>';
                    } else {
                        var a = '<span>' + value + '</span>';
                    }
                    return a;
                },
            }, {
                field: 'modu_name',
                title: '模块名称',
                formatter: function (value, row, index) {
                    if (row.disable_time != null) {
                        var a = '<span style="color:red;">' + value + '</span>';
                    } else {
                        var a = '<span>' + value + '</span>';
                    }
                    return a;
                },
            }, {
                field: 'modu_url',
                title: '模块url',
                visible: false,
                formatter: function (value, row, index) {
                    var val = (value == null ? '-' : value);
                    if (row.disable_time != null) {
                        var a = '<span style="color:red;">' + val + '</span>';
                    } else {
                        var a = '<span>' + val + '</span>';
                    }
                    return a;
                },
            }, {
                field: 'modu_type_name',
                title: '模块类型',
                visible: false
            }, {
                field: 'modu_app_name',
                title: '移动端模块',
                visible: false,
                formatter: function (value, row, index) {
                    if (row.modu_app_name == null) {
                        var a = '否';
                    } else {
                        var a = value;
                    }
                    return a;
                }
            }, {
                field: 'modu_ico',
                title: '模块图标',
                visible: false
            }, {
                field: 'modu_app_ico',
                title: '移动端图标',
                visible: false
            }, {
                field: 'modu_desc',
                title: '模块描述',
                formatter: function (value, row, index) {
                    var val = (value == null ? '-' : value);
                    if (row.disable_time != null) {
                        var a = '<span style="color:red;">' + val + '</span>';
                    } else {
                        var a = '<span>' + val + '</span>';
                    }
                    return a;
                },
            }, {
                field: 'create_user_id',
                title: '创建人id',
                visible: false
            }, {
                field: 'creator',
                title: '创建人',
                formatter: function (value, row, index) {
                    if (row.disable_time != null) {
                        var a = '<span style="color:red;">' + value + '</span>';
                    } else {
                        var a = '<span>' + value + '</span>';
                    }
                    return a;
                },
            }, {
                field: 'create_time',
                title: '创建时间',
                formatter: function (value, row, index) {
                    if (row.disable_time != null) {
                        var a = '<span style="color:red;">' + value + '</span>';
                    } else {
                        var a = '<span>' + value + '</span>';
                    }
                    return a;
                },
            }, {
                field: 'disable_time',
                title: '停用时间',
                visible: false,
                formatter: function (value, row, index) {
                    var val = (value == null ? '-' : value);
                    if (row.disable_time != null) {
                        var a = '<span style="color:red;">' + val + '</span>';
                    } else {
                        var a = '<span>' + val + '</span>';
                    }
                    return a;
                },
            }]
        });