Bump gulp-cache version for rename bugfix

Fixes #151.

This is an issue with `gulp-cache` itself. See jgable/gulp-cache#27 and the pull request at jgable/gulp-cache#28.

Bump the `gulp-cache` version in `package.json` to `~0.2.0` to include this bugfix.
Merge pull request #166 from deefour/patch-1

Bump gulp-cache version for rename bugfix