cmd/protoc-gen-go: --version should exit 0
cmd/protoc-gen-go: --version should exit 0

Fixes golang/protobuf#1153.

Change-Id: Id2ada2353413c3371e677dcf3fdfa6fdc24a3c56
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/239339
Reviewed-by: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>

protocolbuffers/protobuf-go,protocolbuffers/protobuf-go