fix bug: -f not working in docfx metadata
fix bug: -f not working in docfx metadata

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