Use \ for line concatenation in overcommit-hook

Appease the Rubocop gods.

Change-Id: Iaefe596d0d352ba90de574b31e46bec0c59719c2
Reviewed-on: http://gerrit.causes.com/37386
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>