bootstrap3 v3.4.1

 * Fixed border-radii for `.select2-dropdown-open.select2-drop-above` (as reported by @rzschech in https://github.com/t0m/select2-bootstrap-css/issues/24#issuecomment-37683695, https://github.com/t0m/select2-bootstrap-css/issues/24#issuecomment-37688176) and `.select2-dropdown in "Bootstrap input groups with addons".
 * Fixed an issue where using Select2 pre v3.4.2 in combination with Bootstrap v3.2.0 and when using Select2 in a "Bootstrap Input Group with Addons" context would result in the original `<select>` element not being hidden.
 * Removed trailing comma in bower.json.
 * Various cleanup regarding the demo pages.
 * Added "Changelog" and "Contributing" sections to readme.
 * Added `grunt watch` for `lib/select2-bootstrap.scss`.