Fix broken HamlLint spec

This was only failing on Travis builds since we don't install
`haml-lint` there.

Change-Id: I21d295e3a92d2ab76c55ef794e6aa04f41cf5e9e
Reviewed-on: http://gerrit.causes.com/42291
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>