List main files explicitly to work with "grunt-wiredep"

Tools like "wiredep" use the bower "main" property to automatically inject css/js in your index.html.

They expect files to be listed explicitly.
With the glob notation, grunt-wiredep does not find the "devicons.css" file.
Merge pull request #53 from olecrivain/patch-1

List main files explicitly to work with "grunt-wiredep"
Thanks for the commit