all: update to grpc.go4.org and grpc-codegen.go4.org package names

Fixes camlistore/go4#30

Change-Id: Id914ac18bb5bed723a14147d239496aa165e1f3a
Reviewed-on: https://go-review.googlesource.com/45272
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
8 files changed