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.

src/PlatformPeg.js

@@ -47,4 +47,4 @@ class PlatformPeg {
 if (!global.mxPlatformPeg) {
     global.mxPlatformPeg = new PlatformPeg();
 }
-module.exports = global.mxPlatformPeg;
+export default global.mxPlatformPeg;