A new twitter icon fix

More improvements on benschwarz/railscamp-13#2

The old twitter code knocked the alignment of the pin sponsor out.
This one doesn't have that problem.
I also upped the twitter icon size and added a hover effect.
![screen shot 2013-05-21 at 10 07 21 pm](https://f.cloud.github.com/assets/430277/541566/7261ac4c-c20f-11e2-8242-2bec5272c075.png)
![screen shot 2013-05-21 at 10 06 23 pm](https://f.cloud.github.com/assets/430277/541565/69b46abc-c20f-11e2-93f5-a7a851d45cc4.png)