Update gerrit commit-msg hook

This is the version that comes with Gerrit 2.5.1 (the version we're
running currently), which is both shinier and ostensibly more robust.

I `:retab`d in vim to convert hard-tabs to spaces, but otherwise this is
exactly what you get with:

  scp -p -P 29418 gerrit.causes.com:hook/commit-msg hooks/commit-msg

Change-Id: Ia9fc02db330ee3ed3733a3452f82a0e235126116
Reviewed-on: https://gerrit.causes.com/19323
Tested-by: Aiden Scandella <aiden@causes.com>
Reviewed-by: Lann Martin <lann@causes.com>