Updating to use loader from grunt-dojo2

[rorticus]

Updating to use helpers from https://github.com/dojo/shim/pull/114 and loader from grunt-dojo2

[bryanforbes]

I don't think downlevelIteration needs to be turned on or the loader configuration removed for has:

• has doesn't need a shim (it takes in promise-like objects, but doesn't create them).
• Downlevel iteration will create a hard dependency on @dojo/shim or put helpers into the global space and the only thing that uses it is some unit tests.
• Removing the loader configuration means we rely on grunt-dojo2's loader which requires @dojo/shim which creates a dev dependency on @dojo/shim (which is circular)
• The only helper that has uses is __exportStar. It doesn't matter if it's using tslib or the patched one from @dojo/shim.

[rorticus]

This doesn't make sense for dojo/has, so closing.