Bad main

@pennyfx the recent changes in `0.2.3` have a regression in the `bower.json` `main`. `main` must only be a single JS file (you can have alternative css files, but its not relative here).

This bootstrap file is basically useless, since its repeated here.

https://github.com/components/CustomElements/blob/0.2.3/src/custom-elements.js#L366-L368

See the 0.2.1 tag

https://github.com/components/CustomElements/blob/v0.2.1/bower.json#L8
https://github.com/components/CustomElements/blob/v0.2.1/custom-elements.js#L6