Fixed modal for Twitter Bootstrap 3

Hi there,

I built an app using Rails Composer and selected Bootstrap 3.
It looks like Rails Composer chose to use this code : [_user.html.erb](https://github.com/RailsApps/rails3-bootstrap-devise-cancan/blob/master/app/views/users/_user.html.erb) which doesn't work properly with Bootstrap 3. This update should fix it.

Regards,