Improve prototype resolution

Author: medikoo

primitive/index.js

@@ -20,8 +20,11 @@ var clear          = require('es5-ext/object/clear')
 module.exports = PrimitiveMap = function (/*iterable, serialize*/) {
 	var iterable = arguments[0], serialize = arguments[1], self;
 	if (!(this instanceof PrimitiveMap)) throw new TypeError('Constructor requires \'new\'');
-	if (isNative && setPrototypeOf) self = setPrototypeOf(new Map(), getPrototypeOf(this));
-	else self = this;
+	if (isNative && setPrototypeOf && (Map !== MapPolyfill)) {
+		self = setPrototypeOf(new Map(), getPrototypeOf(this));
+	} else {
+		self = this;
+	}
 	if (iterable != null) iterator(iterable);
 	if (serialize !== undefined) {
 		callable(serialize);