Update grunt-css-flip to 0.4.0 which uses the newer css-flip 0.5.0.  Use the RTL style sheet.

Hi Bas,

Updating the version of css-flip seems to have improved things:

![2014-07-28 13_42_18-moodle 27](https://cloud.githubusercontent.com/assets/1058419/3720464/0c150222-1655-11e4-9465-5b87ae9eb71e.png)

Patch also uses the RTL file.

Cheers,

Gareth