Convert CommonJS exports to ES6-compatible exports

We use `export default` begrudgingly here. Ideally we'd use just `export`, though this entire SDK expects things to be exported as a default. Instead of breaking everything, we'll sacrifice our export pattern for a smaller diff - a later commit can always do the default export -> regular export conversion.

test/components/stub-component.js

@@ -4,7 +4,7 @@
 import React from 'react';
 import createReactClass from 'create-react-class';
 
-module.exports = function(opts) {
+export default function(opts) {
     opts = opts || {};
     if (!opts.displayName) {
         opts.displayName = 'StubComponent';