Clearer iteration through keys

- We needed to closure the variable `levels` and this is cleaner

js/log.js

@@ -14,8 +14,7 @@ var levels = {
   'fatal': 5
 };
 
-for (_level in levels) {
-  (function(level) {
+Object.keys(levels).forEach(function(level) {
   Logger.prototype[level] = function() {
     if (levels[level] >= levels[this.level]) {
       var str = '[' + level + '] ' + this.name + ': ' + arguments[0],
@@ -32,8 +31,7 @@ for (_level in levels) {
       }
     }
   };
-  })(_level);
-}
+});
 
 Logger.prototype.setLevel = function(level) {
   this.level = level;