do not show the mobile dropcaps on desktop when the dropcaps--wide class...

This fixes an issue raised by Chris - when a piece of content has not been marked up with with dropcap--wide class ( for breakpoints of desktop and wider ), don't show the mobile drop cap. Which results in the example below: 

![dropcap-desktop-error](https://cloud.githubusercontent.com/assets/986155/2983606/be1395c4-dc26-11e3-9560-5c39627b6212.png)

Fix: 

![dropcap-desktop-fix](https://cloud.githubusercontent.com/assets/986155/2983608/c8ddda82-dc26-11e3-8e25-267dea7e5313.png)