可能会遇到的问题：
Both Entity Framework 6.x and Entity Framework Core commands are installed. The Entity Framework 6 version is executing. You can fully qualify the command to select which one to execute, 'EntityFramework\Update-Database' for EF6.x and 'EntityFrameworkCore\Update-Database' for EF Core.
解决方法：
EntityFrameworkCore\Add-Migration InitialDb
EntityFrameworkCore\Update-Database