Updated package.json with gulp dependencies

The gulpfile.js has been modified in commit 0ccd435 and some new dependencies where introduced. The package.json doesn't list them, I added the most recent version. And since gulp itself is under heavy development whenever there is an update I'll receive a warning on the command line:

```
[gulp] Warning: gulp version mismatch:
[gulp] Running gulp is 3.6.2
[gulp] Local gulp (installed in gulpfile dir) is 3.4.0
```

So I changed the gulp version to just "3".