Change: Upgrade Typhoeus version

Change: Version 0.5.x of Typhoeus does not support cache. Version >0.6.2 does.

https://github.com/typhoeus/typhoeus/blob/master/CHANGELOG.md

I had some need for a newer version of Typhoeus. So here are a couple changes that will allow cloud_assets to play nice with Typhoeus 0.5.x

The bad thing about this version of Typhoeus is that they removed caching. But then it's brought back again in version 0.6.2. So if caching is important, than maybe consider ignoring this PR or else investigate compatibility w/ cloud_assets and 0.6.x. The only reason I didn't is because I have other gems that don't work with Typhoeus 0.6, and I didn't want to spend any more time investigating.