Error when running from a path that contains spaces.

Hi. Thanks for your work on this!

We ran into the following error when running the hamlbars task within a path structure that contains spaces:

    Running "hamlbars:templates" (hamlbars) task
    Warning: Error executing hamlbars on /Users/seejee/code/has spaces/lesson-player/app/templates/blank-view.hamlbars:
    undefined
    sh: /Users/seejee/code/has: No such file or directory
        Use --force to continue.

The attached commit should resolve the issue by wrapping the path with double quotes.