move the contributing hook into hack, and use curl in the same way as the gofmt above

and remove the fmt-check one we don't document

tianon tells me they're called GitHub, not Github :)

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Merge pull request #3542 from SvenDowideit/curl-prepare-commit-msg

move the contributing hook into contrib, and use curl in the same way as the gofmt above