hi_andre highlight fix for OS 10/Homebrew

On Mac OS 10 **highlight** is usually installed in `/usr/local/bin` when it is installed by Homebrew. 

This patch allows users to call `hi_andre` if highlight is in `/usr/local/bin` on Mac OS 10.
Merge pull request #2 from christophergandrud/master

hi_andre highlight fix for OS 10/Homebrew