Release wf-grunt 0.4.0

PRs contained in this release:

https://github.com/WebFilings/wf-grunt/pull/14


Diff Between Last Tag and Proposed Release: https://github.com/Webfilings/wf-grunt/compare/0.3.3...Release_0.4.0

How To +10/QA
-------------

```bash
# skip the following steps if you've already initialized the project
git clone git@github.com:WebFilings/wf-grunt.git
cd wf-grunt

# do not skip these!
git fetch && git checkout Release_0.4.0
Run unit tests
```