Fixes icon font issue

Inserts [missing quotation mark](https://github.com/Codiad/Codiad/blob/master/themes/default/fonts.css#L138) after PR #745. Happens only in FF, not in Chrome.

Before: 
![before](https://cloud.githubusercontent.com/assets/4389878/5554541/15c62daa-8c61-11e4-8ce0-83d5a1abfbbd.png)

After: 
![after](https://cloud.githubusercontent.com/assets/4389878/5554542/1b048eba-8c61-11e4-813e-1572884dd885.png)