Fixed broken RegExp implmentation

Author: Benoit Sagols

lib/memory-backend.js

@@ -68,9 +68,14 @@ MemoryBackend.prototype = {
       .end();
 
     var match;
-    for(var b in this._buckets){
-        var regex = new RegExp("^"+b+"$");
-        if(bucket.match(regex)) bucket = b;
+    var re;
+    if (!this._buckets[bucket]) {
+      Object.keys(this._buckets).some(function(b) {
+        re = new RegExp("^"+b+"$");
+        match = re.test(bucket);
+        if (match) bucket = b;
+        return match;
+      });
     }
 
     if(this._buckets[bucket]){