Workaround a recent behavior modification

A fresh `npm install` seems to break the `build` task. It used to work fine on my laptop but broke after a reset of `node_modules`.

```
$ grunt build
[ snip ]
>> Uglifying source "dist/app/app.js" failed.
Warning: Uglification failed.
Unexpected token: name (stores). 
Line 61327 in dist/app/app.js
 Use --force to continue.

Aborted due to warnings.
```

The offending line is https://github.com/torkelo/grafana/blob/master/src/app/app.js#L29, which has been uncommented by a previous task, hence the error.

My fix is quite naive, there must be a better way… I haven't found the 3rd-party library version change that caused the issue though.

Here's my `npm list`: https://gist.github.com/brutasse/e1d158792531db2c00cb