capping tonal contributor image size

before
======
![image](https://cloud.githubusercontent.com/assets/960919/3285732/a8ef6b56-f53e-11e3-9a4c-9ed5e57af599.png)

after
====
![image](https://cloud.githubusercontent.com/assets/960919/3285734/ba26f286-f53e-11e3-9a30-ddc8978a4804.png)

thanks!