Don't depend on haml-contrib in tests.
Don't depend on haml-contrib in tests.

I recently added a rescue from LoadError if the Maruku and Textile
filters from haml-contrib aren't available. Since we don't test those
filters here, there's no longer any need to depend on haml-contrib even
for development.

See issue #551

[ci skip]

haml/haml,macressler/haml,haml/haml,keithpitty/haml,keithpitty/haml,dg1dd1ngs/haml,nazar-pc/haml,tangposmarvin/haml,macressler/haml,stanhu/haml,haml/haml,tangposmarvin/haml,haml/haml,nazar-pc/haml,amatsuda/haml,dg1dd1ngs/haml,stanhu/haml,sideci-sample/sideci-sample-haml