better closure variable name in default parameters

lib/6to5/transformation/transformers/es6-default-parameters.js

@@ -11,7 +11,7 @@ exports.Function = function (node, parent, file, scope) {
     return t.getIds(param);
   });
 
-  var closure = false;
+  var iife = false;
 
   _.each(node.defaults, function (def, i) {
     if (!def) return;
@@ -29,7 +29,7 @@ exports.Function = function (node, parent, file, scope) {
         }
 
         if (scope.has(node.name)) {
-          closure = true;
+          iife = true;
         }
       };
 
@@ -40,7 +40,7 @@ exports.Function = function (node, parent, file, scope) {
     // we're accessing a variable that's already defined within this function
     var has = scope.get(param.name);
     if (has && !_.contains(node.params, has)) {
-      closure = true;
+      iife = true;
     }
   });
 
@@ -55,7 +55,7 @@ exports.Function = function (node, parent, file, scope) {
     }, true));
   });
 
-  if (closure) {
+  if (iife) {
     var container = t.functionExpression(null, [], node.body, node.generator);
     container._aliasFunction = true;