make class methods unenumerable - fixes #41

test/fixtures/classes/instance-method/expected.js

@@ -1,8 +1,13 @@
 var Test = function () {
   function Test() {
   }
-  Test.prototype.test = function () {
-    return 5 + 5;
-  };
+  Object.defineProperties(Test.prototype, {
+    test: {
+      writeable: true,
+      value: function () {
+        return 5 + 5;
+      }
+    }
+  });
   return Test;
 }();