Removing nokogiri dependency

and trimming down the Dockerfile a bit while I'm in there.
Just a smidge more cleanup around prereq install
Attempting to switch to a standalone Dockerfile that pulls from S3
Merge pull request #9 from modcloth-labs/standalone-dockerfile

Attempting to switch to a standalone Dockerfile that pulls from S3
Merge pull request #6 from modcloth-labs/bye-bye-nokogiri

Removing nokogiri dependency