Uses unlicensed opentracing-contrib/go-grpc

[asuffield]

server/server.go imports github.com/opentracing-contrib/go-grpc

This repo doesn't have a license (opentracing-contrib/go-grpc#3), so this makes weaveworks/common unusable for us.

go-grpc looks trivial, so if getting it licensed is somehow hard, it would probably not take very long to rewrite...

[bboreham]

Thanks for raising this.
The code in that package was from https://github.com/grpc-ecosystem/grpc-opentracing, which does display a licence. I think we can assume this is an oversight in copying files rather than a real lack of licence.

I'll try again to make contact with its maintainers.

[dholbach]

The upstream issue is now fixed. Can we update our dep?