SSO: Adjust size of WP logo on forced SSO button. Fixes #1166

The last time I tried to adjust an SSO button, it wasn't as perfect as it should be. I *think* this one does a better job. 
![screen shot 2014-10-08 at 22 05 53](https://cloud.githubusercontent.com/assets/88897/4570581/3803c7fc-4f61-11e4-8699-f093b6cef718.png)