Exclude bower_components directory by default :)

[shivapoudel]

If the people are using bower too they they may forgot to exclude bower_components so it's better to add this by default.

[bradyvercher]

Hey @shivapoudel, I appreciate the PR, but I'm reluctant to add any more directories to the default list. In this particular case, if someone wanted to include strings from a package pulled in by Bower, this would make it difficult to do so.