googlemap plugin: Bootstrap and Google Maps Info window styles problem

Current bootstrap styles have an issue with google maps ones, affecting info window appearance. 

As this fix does not affect any other style, maybe would be a good idea to fix it at django-cms side. maybe not ;)

Issue is currently opened in bootstrap:
twitter/bootstrap#2410

The pull request is a quick fix got from referenced bootstrap issue

![gmap-bootstrap-infow-issue](https://f.cloud.github.com/assets/797664/431124/a4b9287a-ae80-11e2-92c5-e04c9749a243.jpg)