Merge pull request cerebral#16 from cerebral/proxyStateTreeObjectMethods

fix(proxy-state-tree): fix issue with accessing Object.prototype methods

Author: christianalfoni

packages/node_modules/proxy-state-tree/src/proxify.ts

@@ -98,7 +98,8 @@ function createObjectProxy(tree, value, path) {
       if (prop === PATH) return path
       if (prop === VALUE) return value
 
-      if (typeof prop === 'symbol') return target[prop]
+      if (typeof prop === 'symbol' || prop in Object.prototype)
+        return target[prop]
 
       const targetValue = target[prop]
       const nestedPath = concat(path, prop)