add a buildNoVersion task to main.js

The reason for this task is so it's easier to specify file options for  [grunt-ember-s3](https://github.com/fivetanley/grunt-ember-s3).

For some ember projects, we will upload a file like `ember-thisIsAGitRevision.js` to S3. Right now, using grunt-ember-s3, it would upload a file like `rsvp-2.0.0-latest.js` and `rsvp-2.0.0-thisIsAGitRevision.js` to S3, which looks a little silly and may be confusing to people downloading the files from s3 (think "there's 2.0.0 and 2.0.0-latest, which should I get?").

This adds a task so that when you run `grunt buildNoVersion`, you would get the following files in the `dist` folder:

```
dist/rsvp.amd.js
dist/rsvp.js
dist/rsvp.min.js
```

Perhaps @stefanpenner could add some input to this as well.