Bump version to 0.6.2

I added Cordova plugin support in dc0549d8d300a27b42ca889cd49f33d2bbf54c91, but it's only useful if it is released, since it currently requires `dist/sip.js` to be used. This PR simply bumps the version numbers in `package.json`, `bower.json`, and `plugin.xml`. I'll create another PR for with the `dist/` files for the actual release.