release.bash: make work on macOS
release.bash: make work on macOS

macOS's sed always considers the parameter following -i to be an
extension, so "-i -e" means "edit in place saving backup with a -e
extension".

macOS's sed does not support \s in regexps.

Change-Id: Ic9b57baa5fc88fff2251c640d11ed417a7257f13
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/322449
Trust: Damien Neil <7e091e9a80da888fcd7836fd3c6b7b85f4677c12@google.com>
Run-TryBot: Damien Neil <7e091e9a80da888fcd7836fd3c6b7b85f4677c12@google.com>
Reviewed-by: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>

protocolbuffers/protobuf-go,protocolbuffers/protobuf-go