Issue description

As part of the .NET 5.0 release, all supported .NET Docker tags will be transitioning from a repository name of mcr.microsoft.com/dotnet/core/* to mcr.microsoft.com/dotnet/*. Basically, "core" is being removed from the name. This applies to all .NET versions (2.1, 3.1, 5.0). See dotnet/dotnet-docker#2337 for more info. All references to these old repository names should be updated to have "core" removed.

Target framework

• .NET Core
• .NET Framework
• .NET Standard

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