Update dotnet-fable.fsproj
Update dotnet-fable.fsproj

Update TargetFramework to point at `netcoreapp1.1`.

I'm trying to use dotnet-fable on a Fedora 24 box and it only supports dotnet core 1.1.

Do you see any issue with bumping the `TargetFramework` here?
fable-compiler/Fable,fable-compiler/Fable,ncave/Fable,ncave/Fable,inosik/Fable,fable-compiler/Fable,fable-compiler/Fable,inosik/Fable,ncave/Fable,ncave/Fable,fable-compiler/Fable,ncave/Fable,fable-compiler/Fable,ncave/Fable,fable-compiler/Fable,ncave/Fable