Options should be optional

Currently if you do not provide options you will get "cannot get property level of undefined"

index.js

@@ -10,6 +10,7 @@ var util = require('util'),
 
 
 var WinstonCloudWatch = function(options) {
+  options = options || {};
   winston.Transport.call(this, options);
   this.level = options.level || 'info';
   this.name = options.name || 'CloudWatch';