Fix app name in staging config

* ".classify" turns "app_name" -> "AppName" but "app-name" -> "App-name"
* Use gsub to turn dashes unto underscores before calling ".classify"
* This makes the app name consistent with how rails converts the app
  name in other config files

Example of what suspenders generated for a rails project named 'gratitude-ember':
![screen shot 2014-04-15 at 2 34 00 pm](https://cloud.githubusercontent.com/assets/601515/2713489/9e6998c8-c4e7-11e3-8cc6-62e77cc56ff1.png)