Fix: Add activeTab permission.

The lack of the activeTab[1] permission was causing the app to fail.

I don't know since when is required, but it was introduced in chrome 26[2]

[1]: https://developer.chrome.com/extensions/activeTab
[2]: https://groups.google.com/a/chromium.org/forum/#!topic/chromium-extensions/P2BA55ahYHM
Bumped version from 1.0.7 to 1.0.8