Makes meteor.sh exit on errors.

As of before, Meteor.sh would give you the success message in the end - "Your app is deployed and ..." even if there was an error in the middle of the process.

This helps fix that, as per this article - http://robertmuth.blogspot.pt/2012/08/better-bash-scripting-in-15-minutes.html.
Merge pull request #16 from davidgomes/patch-1

Makes meteor.sh exit on errors.