Add babel to dependencies

[milindalvares]

Takes care of the deprecation warning:

DEPRECATION: Addon files were detected in /Users/milindalvares/dev/invoicesapp-frontend-ember/node_modules/ember-cli-copyable/addon, but no JavaScript preprocessors were found for ember-cli-copyable. Please make sure to add a preprocessor (most likely ember-cli-babel) to in dependencies (NOT devDependencies) in ember-cli-copyable's package.json.

As discussed in Issue #24.