Add support for CDN build in Gruntfile

The CDN build only includes minified Cilantro files without source
maps and third-party libraries.

Modernizr has been removed since it is not a dependency of Cilantro
itself. Host projects should include it if older browsers need to be
supported and HTML5 features are being used.

Signed-off-by: Byron Ruth <b@devel.io>
Merge pull request #507 from cbmi/cdn-gruntfile

Add support for CDN build in Gruntfile