ESM format issues

It seems that `index.js` in current 2.4.2 version is not a proper ES module, even though it appears to be intended as one.

The file still has CommonJS semantics, like `require` and `exports.default`.

When I try to use it in my ESM environment, importing `import wiki from 'wikipedia';` doesn't work.

It returns an object with `default` in it and I need to unwrap it to access functions like `page`.