Fix the lost ratio problem.

If the bitmap's ratio is not fit ImageView's ratio.
rq.fit() will cause the bitmap to be stretched to fit the imageView,it looks so ugly.

so .fit().centerCrop() can sovle the problem.

see below.
![screenshot_2014-06-10-16-40-36](https://cloud.githubusercontent.com/assets/2627625/3227468/5aa37590-f07b-11e3-8026-1f8d73374d08.png)
![screenshot_2014-06-10-16-41-23](https://cloud.githubusercontent.com/assets/2627625/3227469/5aa78784-f07b-11e3-8606-5ed4d861b978.png)