Add MessageDisplayKit.podspec v0.1.2

smoe error:
Can't find the classes.

Thanks you for you help.

![7bb86dd0-25f8-43f8-bfc0-1c37593b6345](https://cloud.githubusercontent.com/assets/1969908/2872120/4d262a5c-d343-11e3-91c0-fb8202d256b3.png)

Jack