grammer change to missing packages on launch

Tweak the message we display when there is a missing package when launching an application:

![screen shot 2014-06-09 at 9 26 57 am](https://cloud.githubusercontent.com/assets/1269969/3219209/4acadede-eff3-11e3-94dd-5c30b9c132d4.png)

@keertip