Update to support grunt 1.0

[amakhrov]

Hi @iammerrick

Looks like you've already merged the PR with the update needed (#40)
Would you mind publishing a new version at npm?

Also looks like apart from peerDependency, you also list grunt as a regular dependency - and this one is still the old version.
To me it seems that the latter can be safely dropped at all - it doesn't seem to be used.
The PR with the proposed change: #42

Thanks!