Reduced docker image size (#51)

* Change Dockerfile base to node:6-alpine
* Replace BusyBox grep (Alpine) with GNU grep
* Update maintainer LABEL
* Use COPY destinations relative to WORKDIR

abh suggestions

Ignore fixme comments in .codeclimate.yml

If you're using custom strings, we'll find those strings in config file
where you specify those custom strings, and create some issues. That
seems less than helpful.

Merge pull request #40 from codeclimate/pb-fix

Ignore unparsable stdout

Merge pull request #36 from ConnerMan/readme-issues-link

Correct GitHub Issues link in README

Merge pull request #35 from codeclimate/jp/update-estlintrc

Use eslintrc.js from styleguide

Merge pull request #34 from codeclimate/jp/improve-coverage

Improve test coverage

Fix Makefile

With a properly set WORKDIR, we need to ensure that we chdir
into the right directory before running the tests.

Merge pull request #32 from codeclimate/jp/tidy-up

Tidy up

Merge pull request #31 from codeclimate/jp/fix-fixme

Invoke grep only once per run