switch back helpers to Array.isArray

src/babel/transformation/templates/for-of-loose.js

@@ -1,5 +1,5 @@
 for (var LOOP_OBJECT = OBJECT,
-         IS_ARRAY = LOOP_OBJECT && LOOP_OBJECT.constructor === Array,
+         IS_ARRAY = Array.isArray(LOOP_OBJECT),
          INDEX = 0,
          LOOP_OBJECT = IS_ARRAY ? LOOP_OBJECT : LOOP_OBJECT[Symbol.iterator]();;) {
   var ID;

src/babel/transformation/templates/helper-sliced-to-array-loose.js

@@ -1,5 +1,5 @@
 (function (arr, i) {
-  if (arr && arr.constructor === Array) {
+  if (Array.isArray(arr)) {
     return arr;
   } else if (Symbol.iterator in Object(arr)) {
     var _arr = [];

src/babel/transformation/templates/helper-sliced-to-array.js

@@ -1,10 +1,10 @@
 (function (arr, i) {
-  if (arr && arr.constructor === Array) {
+  if (Array.isArray(arr)) {
     return arr;
   } else if (Symbol.iterator in Object(arr)) {
     // this is an expanded form of `for...of` that properly supports abrupt completions of
     // iterators etc. variable names have been minimised to reduce the size of this massive
-    // helper. sometimes spec compliancy is annoying :()
+    // helper. sometimes spec compliancy is annoying :(
     //
     // _n = _iteratorNormalCompletion
     // _d = _didIteratorError

src/babel/transformation/templates/helper-to-array.js

@@ -1,3 +1,3 @@
 (function (arr) {
-  return arr && arr.constructor === Array ? arr : Array.from(arr);
+  return Array.isArray(arr) ? arr : Array.from(arr);
 });

src/babel/transformation/templates/helper-to-consumable-array.js

@@ -1,5 +1,5 @@
 (function (arr) {
-  if (arr && arr.constructor === Array) {
+  if (Array.isArray(arr)) {
     for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) arr2[i] = arr[i];
     return arr2;
   } else {