Update `RELEASE.md` instructions to avoid having two release commits
Update `RELEASE.md` instructions to avoid having two release commits

Currently, the release instructions in `RELEASE.md` tell you to
update `version.rb`, commit that change and then run
`script/release -r`, which also makes a commit itself.

This tweaks the instructions so you just update the version and
then run the release script, meaning you just get one clean
commit.

octokit/octokit.rb,octokit/octokit.rb