Documentation: update broken wire.html link in metadata package. (#1791)
Documentation: update broken wire.html link in metadata package. (#1791)

https://grpc.io/docs/guides/wire.html is no longer valid.

Looking at an archived version of that page
(https://web.archive.org/web/20171006045517/https://grpc.io/docs/guides/wire.html)
it looks equilavent to what is now posted at:
https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md.

The gRPC guide: https://grpc.io/docs/guides/ contains a link in the
sidebar navigation to the same page, so pretty sure it's correct.
rakyll/grpc-go,menghanl/grpc-go,stanley-cheung/grpc-go,rakyll/grpc-go,MakMukhi/grpc-go,grpc/grpc-go,improbable-io/grpc-go,MakMukhi/grpc-go,thinkerou/grpc-go,dfawley/grpc-go,peter-edge/grpc-go,improbable-io/grpc-go,peter-edge/grpc-go,stanley-cheung/grpc-go,menghanl/grpc-go,grpc/grpc-go,dfawley/grpc-go,thinkerou/grpc-go