Fix broken esm import

[rubicon2]

Solves issue #27

As per the typescript docs:

Users will detect a misconfigured module smell if they have to access the .default property of a default import, and if they’re trying to write code that will run both in Node.js and a bundler, they might be stuck. Some third-party TypeScript transpilers expose options that change the way default exports are emitted to mitigate this difference, but they don’t produce their own declaration (.d.ts) files, so that creates a mismatch between the runtime behavior and the type checking, further confusing and frustrating users. Instead of using default exports, libraries that need to ship as CommonJS should use export = for modules that have a single main export, or named exports for modules that have multiple exports...

I have made this change, so now esm imports (import/export) and commonjs imports (require) will both work.

However, I had to change the import in the test file from require('../dist').default to require('../dist'), so I guess that would break the import for existing users that are using .default.

[rubicon2]

I have been trying this out with bundlers to see if it all works, and it turns out this also fixes a broken import when importing with require() and bundling with webpack. Importing with esm syntax and bundling actually worked fine already.

I don't understand why the esm syntax worked when bundling, but not with an express app I was working on. I guess webpack transpiled the code into something that works??