ES6 Modules with grant
Hi. Thanks for making `grant`. I tried it and it works well for many OAuth2 providers. 

One question I had was regarding support for ES Modules. While I understand from the issues that you have decided not to support Typescript, I was wondering how to import grant as a ES6 module.

While `require('grant').fastify();` works, I wanted to go the standard route since `require` is not a standard and definitely not recommended in the future for Node.js with `mjs` support now in place.