use commonInterop module formatter in 6to5/register

lib/6to5/register.js

@@ -72,7 +72,8 @@ var loader = function (m, filename) {
   var result = to5.transformFileSync(filename, {
     whitelist: whitelist,
     blacklist: blacklist,
-    sourceMap: true
+    sourceMap: true,
+    modules:   "commonInterop"
   });
 
   maps[filename] = result.map;