update cross reference part of metadata spec
update cross reference part of metadata spec

pascalberger/docfx,LordZoltan/docfx,sergey-vershinin/docfx,pascalberger/docfx,pascalberger/docfx,superyyrrzz/docfx,sergey-vershinin/docfx,hellosnow/docfx,DuncanmaMSFT/docfx,928PJY/docfx,LordZoltan/docfx,LordZoltan/docfx,hellosnow/docfx,superyyrrzz/docfx,hellosnow/docfx,dotnet/docfx,928PJY/docfx,superyyrrzz/docfx,DuncanmaMSFT/docfx,sergey-vershinin/docfx,dotnet/docfx,928PJY/docfx,dotnet/docfx,LordZoltan/docfx