Fix gulp build task.

[XhmikosR]

No description provided.

[XhmikosR]

I'm gonna close this and make a PR to add Travis. @feimosi: can you add Travis CI to this repo and I'll add the needed stuff in a new PR.

[feimosi]

Sure, no problem.
Just the gulp task could be written like this:

gulp.task('build', runSequence(['css', 'js', 'css-min', 'js-min'], 'update-version'));

Notice the array. These can run in parallel.

[XhmikosR]

But css-min needs css. Anyway see #91.