public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    services.AddEntityFramework()
        .AddSqlServer()
        .AddDbContext<EfDbContext>(options =>
        {
            options.UseSqlServer(Configuration.Get("Data:ConnectionString"));
        });
}

error CS1061: 'EntityFrameworkServicesBuilder' does not contain a definition for 'AddSqlServer' and no extension method 'AddSqlServer' accepting a first argument of type 'EntityFrameworkServicesBuilder' could be found (are you missing a using directive or an assembly reference?)