use WeakMap for AST node cache

Author: eush77

index.js

@@ -1,14 +1,14 @@
 'use strict';
 
-var Map = require('es6-map');
+var WeakMap = require('es6-weak-map');
 
 
 module.exports = function (ast) {
   return wrapNode(ast, null);
 };
 
 
-var cache = new Map;
+var cache = new WeakMap;
 
 function wrapNode (node, parent) {
   if (cache.has(node)) {

package.json

@@ -30,7 +30,7 @@
     "walk"
   ],
   "dependencies": {
-    "es6-map": "^0.1.1"
+    "es6-weak-map": "^2.0.1"
   },
   "devDependencies": {
     "clone": "^1.0.2",