Fix typo in grunt verison

There is a typo in the version of grunt, the version was called '0.4.0-rc3' not '0.4.0rc3'. You possibly want to upgrade to a later version of grunt now, but I wanted to just fix the typo, as it creates problems on some versions of npm, particulary `1.2.18`.

See https://github.com/TryGhost/Ghost/issues/1787