Set subscribe bar height to 20px (+10px padding) to match the new dropbox

See issue  #50. This makes the new dropdown box in the subscribe menu fix in Firefox.

Before:

![screen shot 2013-10-10 at 7 49 38 pm](https://f.cloud.github.com/assets/1447206/1311741/cbf8aebc-3218-11e3-9330-51b5d36574aa.png)

After:

![screen shot 2013-10-10 at 8 00 14 pm](https://f.cloud.github.com/assets/1447206/1311745/ed73e610-3218-11e3-939b-c3d7c71043f7.png)

Chrome and Safari look the same.