Fail on lint error

I saw that my previous PR introduced linting error [on travis ci](https://travis-ci.org/davidebukali/Ukansearch/builds/30622392). With this fix I make sure that in the future the build fails in such cases (by adding the `jshint.reporter('fail')`) and that the previous error is fixed by ignoring `bower_components` (as we don't care if a 3rd party library violates the linting rules).