Made error message more verbose, when unable to run the generate command

I had the same issue as in https://github.com/gnarula/sublime-laravelgenerator/issues/17

So I decided to include the output of the process when the generate command fails to run.

![Screen Shot 2013-04-24 at 2 07 13 PM](https://f.cloud.github.com/assets/220535/421559/a63aec36-ad0b-11e2-9d6f-69d883e43b96.PNG)