Update Dockerfile

to get past the first error of "no command specified", could either do this or add a command in the 'cmd' section of the Vagrantfile's docker provider section.  that 'no command specified' error was coming from docker itself, you'd see that same error if you tried building and running the original dockerfile directly in docker, even if you weren't going through vagrant
Merge pull request #1 from lukewpatterson/patch-1

Update Dockerfile