check package version before buildt

This is the PR mention in #6. I also added the bower update argument `---production` to svg.js. It doesn't do anything now but it might in the future and we probably never need anything but the `svg.js` file itself.

This PR is a cumulative PR. Let me know if you want to reject #5 and only merge the version check. Then I'll update this PR.

I've also made a feature request with https://github.com/yatskevich/grunt-bower-task/issues/103 about not copying svg.js everytime you do a `grunt update`. We'll see what happens. Unfortunately I don't have time to pursue this further until next week.