Update lib/hem-haml-coffee.js

Changed HamlCoffee require path to use src/ instead of lib/ to work with newer versions of haml-coffee.

lib/hem-haml-coffee.js

@@ -1,5 +1,5 @@
 var hem  = new (require('hem'));
-var HamlCoffee = require('haml-coffee/lib/haml-coffee');
+var HamlCoffee = require('haml-coffee/src/haml-coffee');
 var CoffeeScript = require('coffee-script')
 var fs   = require('fs');
 var argv = process.argv.slice(2);