Fix grunt dependencies for npm 2.0.0

[brittanydionigi]

This should resolve the install issue opened at mozilla/recroom#41 Though there are still significant issues with npm 2.0.0 that are being worked out. (npm/npm#6043 / https://twitter.com/othiym23/status/507042794997682176)

Everything should still work as expected when using with npm 1.4.26 but would like somebody else to test out as well.

[brittanydionigi]

Also, this just in:

othiym23> brittanstoroz: we may or may not revert the change (npm/npm@ea547e2) before the final release of 2.0.0, depending on how that thread (semver/semver#221) plays out

So maybe let's wait on this.

[fwenzel]

Looks like you're mostly upgrading dependencies, right? Is it going to re-break if they back out that change? If so, let's wait. If not, then we'd probably be fine landing this anyway. (But I'll leave it to @tofumatt to make that call)

[brittanydionigi]

Right - It shouldn't re-break if they back out of the change - I tested it out in 1.4 and everything worked as usual. But yes, would like to see if @tofumatt knows of anything off the bat that might make this problematic.

[vladikoff]

We saw this issue a few days ago, the only dependency that you need to update is grunt-contrib-uglify, see this PR #19

[brittanydionigi]

Closing this in favor of @vladikoff's simpler solution which also resolves the issue.