Centered 2015 logo on tag

From: 
![image](https://cloud.githubusercontent.com/assets/1341391/4752095/120b7aee-5aa7-11e4-8f7e-ab89e57e2e56.png)

To:
![image](https://cloud.githubusercontent.com/assets/1341391/4752099/1b30bfb2-5aa7-11e4-9f76-1f5d29c97337.png)