v3.0.0

Even though the #7 fix is a bug fix, this will end up being a breaking change if anybody has been relying on the silent success for a case when writeFile fails. Thus, this is a major version bump.

• Make sure to reject the promise if writeFile errors (#7)
• All grade A-supported node/iojs versions now ship with an npm that understands ^
• Speed up travis-ci builds; test on latest node and io.js versions
• Update is, jscs, tape