Upgrade to 2.21
Upgrade to 2.21

pascalberger/docfx,superyyrrzz/docfx,superyyrrzz/docfx,hellosnow/docfx,DuncanmaMSFT/docfx,pascalberger/docfx,pascalberger/docfx,dotnet/docfx,dotnet/docfx,dotnet/docfx,928PJY/docfx,hellosnow/docfx,DuncanmaMSFT/docfx,hellosnow/docfx,928PJY/docfx,928PJY/docfx,superyyrrzz/docfx