Switches to the official Highlight.js module

The highlight module being used previously is a 
little quirky out of the box (for me, it was only
loading PHP by default and actually didn't have 
CoffeeScript present at all). 

Additionally, even with the official module, my
CoffeeScript is usually detected as if it were 
Perl (I'm not sure what this says about me), so
I wanted to continue supporting named code blocks
(e.g. ``` coffeescript)