Adds phantomjs to docker container PATH

[willfish]

What?

Adds phantomjs to the docker container path as I was being prompted to add phantomjs to my path in the old version and now I get a list of failures (think koans) that need to be fixed when I run docker-compose run web rails training

Also lints a bunch of things in the Dockerfile:

• Use COPY instead of ADD
• Don't install additional packages
• Remove package lists to make container smaller
• Renames from myapp to goat for fun

Why?

So that I can successfully complete the koans

A/C

Enables successful running of koans