style(npmignore): add bower_components folder to ignore list

[americoneto1]

PR to exclude bower_components folder when publish packages to NPM registry, it´s related to #1683

[nateabele]

Make sure you follow the contributor guidelines when submitting PRs. Here's a handy little checker: http://prjs.radify.io/#/angular-ui/ui-router/pulls/2498

[americoneto1]

Thanks @nateabele ! I updated PR subject, it's ok now?

[nateabele]

It's based on the actual commit message, not the PR title (I keep forgetting to update the PR hinting tool, sorry). It's for our changelog generator, otherwise things get all wonky.

[christopherthielen]

To fix the commit message:

• Use interactive rebase: git rebase -i
• When the editor opens, change the commit from pick to r for "reword".
• Change the commit message to match the contributor guidelines, save and quit.
• Force push to the PR branch git push --force

[nateabele]

Merged manually: 508f9ce