Default exports with parens fails #421

Via rollup/rollup-plugin-babel#28.

This fails:

// main.js
import foo from './foo.js';
foo();

// foo.js
export default (function () {
  console.log("Hi!");
})

Remove the parens around the default export and it works fine. It appears to be specific to functions (this works fine).

This is particularly problematic because this is how Babel transpiles arrow function expressions.