fix(launcher): allow afterLaunch to run async scripts

I'm not sure that it will hang - for example, the following script exits immediately:

```
var q = require('q');

console.log('starting');

var deferred = q.defer();

deferred.promise.then(function() {
  console.log('done!'); // this is never printed.
});
```

Since there aren't currently good failure-case tests or unit tests for launcher, I'd feel better if the check was still there.