remove 'app.config' from 'docfx.Tests.csproj'
remove 'app.config' from 'docfx.Tests.csproj'

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