Use safe colors to avoid header problems

Use the safe mode of the "colors" module.
Extending the string prototype leads to problems
with union's way of setting HTTP headers.

bin/http-server

@@ -2,7 +2,7 @@
 
 'use strict';
 
-var colors     = require('colors'),
+var colors     = require('colors/safe'),
     os         = require('os'),
     httpServer = require('../lib/http-server'),
     portfinder = require('portfinder'),