properly handle export default shorthand, also consider export default foo; and export { foo as default } to be equivalent

test/core/fixtures/transformation/es7-export-extensions/default-commonjs/expected.js

@@ -1,9 +1,5 @@
 "use strict";
 
-Object.defineProperty(exports, "__esModule", {
-  value: true
-});
-
 var _foo = require("bar").foo;
 
-exports.foo = _foo;
+module.exports = _foo;

test/core/fixtures/transformation/es7-export-extensions/default-es6/expected.js

@@ -1,4 +1,4 @@
 "use strict";
 
 import { foo as _foo } from "bar";
-export { _foo as foo };
+export { _foo as default };