Update dependencies

A few dependencies were updated.

Update dependencies; require node.js >= 4.x; added CI

Update package to 0.4.0, raised min dep of node.js to 4 due to
dependencies (proven through CI: cannot support 0.12.0 due to
the dependency chain), and add AppVeyor and Travis CI builds.
Updated the readme with build badges.

Remove exec-sync dependency.

Removed exec-sync per #42 (https://www.npmjs.com/advisories/310)

Bump version to 0.3.12

Fix execSync dep

0.3.2

Version bump

Fix the :kill task on UNIX and Windows

Thanks to @SergKr for the PR.