make minification.renameLocalVariables work

lib/6to5/transformation/transformers/minification/rename-local-variables.js

@@ -2,10 +2,8 @@
 
 exports.optional = true;
 
-exports.Scope = function () {
-  // todo: get all binding identifiers, generate compact names
-  // that wont collide and then call the remap identifier helper
-
-  // this transformer **has** to be ran last as it will absolutley
-  // destroy the scope tree
+exports.Scopable = function (node, parent, scope) {
+  //for (var name in scope.bindings) {
+  //  scope.rename(name, scope.generateUidIdentifier("a").name);
+  //}
 };