Jetpack: SSO: Fix a minor styling glitch where pre-3.8 versions get the wrong size blue addition to the SSO button on the login page, and it could look like this:

https://cloudup.com/cMBnlB6TYgl



git-svn-id: https://plugins.svn.wordpress.org/jetpack/trunk@810966 b8457f37-d9ea-0310-8a92-e5e31aec5664