Fixed calculator layout for pre-L

The calculator buttons were small in Kitkat, fixed it to fit the layout.

Old
![device-2014-10-25-144257](https://cloud.githubusercontent.com/assets/866735/4779037/b670b0d8-5c12-11e4-83d0-b6a2c5cf90a8.png)

New
![device-2014-10-25-144321](https://cloud.githubusercontent.com/assets/866735/4779038/b95a6924-5c12-11e4-8970-f494b84d1b84.png)
I thought the same as well, but see screenshot below. The difference is very minor.

Old
![screenshot_2014-10-26-02-43-46](https://cloud.githubusercontent.com/assets/866735/4780759/3a705118-5c77-11e4-9257-cc1812a7da61.png)

New
![screenshot_2014-10-26-02-44-00](https://cloud.githubusercontent.com/assets/866735/4780760/3fd5a3e2-5c77-11e4-9acd-5fa6b55cdade.png)