ignore member expressions in constants transformer - fixes #770

lib/6to5/transformation/transformers/es6/constants.js

@@ -10,6 +10,8 @@ exports.check = function (node) {
 var visitor = {
   enter: function (node, parent, scope, state) {
     if (t.isAssignmentExpression(node) || t.isUpdateExpression(node)) {
+      if (t.isMemberExpression(node.left || node.argument)) return;
+
       var ids = t.getBindingIdentifiers(node);
 
       for (var name in ids) {