jasmine-node expects and array of `specFolders`

When setting `projectRoot` and `specNameMatcher` in grunt config jasmine node expects and array.

See:
https://github.com/mhevery/jasmine-node/blob/master/lib/jasmine-node/spec-collection.js#L19
https://github.com/mhevery/jasmine-node/blob/master/lib/jasmine-node/index.js#L71