Fix regex. Now it shows OS X and other Oses name correctly.

Betty shows Linux when it runs on OS X and it is due of incorrect regex.
![incorrect_result](https://cloud.githubusercontent.com/assets/4386285/2956158/95db305a-da8a-11e3-8ffa-04bae08f900b.png)

Add some other major OSes that betty could run on them.