Change anypb.Any to emptypb.Empty (thanks @danw for the fix)

[ntaylor-barnett]

This fixes a issue that was picked up in some of my own unit tests for a separate project. Thanks danw for the workaround. I don't know for sure if this will cause problems for other people, but it got it all working perfectly in my use cases.

https://github.com/mwitkow/grpc-proxy/issues/55#issuecomment-1059557772

[stdll00]

In my case, also need fix L147 &anypb.Any{} to &emptypb.Empty{}.

[dlakshma]

Is this fix from anypb to emptypb will be merged to main branch. If fixes the invalid utf-8 error when response is received from grpc-proxy