Fix not looping issue in uix/video.py

Refers to this issue: https://github.com/kivy/kivy/issues/1268

I also found this, fixed it, submitted a PR, but then withdrew it because the "eos" properties are confusing. "eos" is a boolean property for VideoPlayer and Video, but a string property in CoreVideo (from kivy.core.video import Video as CoreVideo). Seems....wrong.

This at least is a minimal fix. But perhaps this should be addressed? Perhaps

    Video(source='video.mpg', state='play', options={'loop': True}))