Fix tests when grunt isn't installed globally.
Fix tests when grunt isn't installed globally.

Checking out the project, running `npm install`, and then running `npm test` fails if grunt isn't installed globally.

Observed with this version of `npm`:
```
$ npm -version
3.10.3
```

Requires https://github.com/wcandillon/swagger-js-codegen/pull/158

wcandillon/swagger-js-codegen,adamstortz/swagger-js-codegen,adamstortz/swagger-js-codegen,wcandillon/swagger-js-codegen