Fix a type for em dash

Hi `&mdash;` is &mdash; and `&emdash;` is &emdash;. It's cool!

:zap: 

cc @hone 

![image](https://cloud.githubusercontent.com/assets/1153134/3485847/c4fd5c1a-0405-11e4-8090-451a76a42b88.png)

:point_down: 

![image](https://cloud.githubusercontent.com/assets/1153134/3485848/ca8aa8ea-0405-11e4-87c5-08299f5ecd88.png)