Support ES6 syntax for botkit features

[cooperka]

Now botkit can handle both CJS module.exports and ESM export default syntax.

Previously only this was supported:

module.exports = function(controller) {
    controller.hears('sample', 'message', async (bot, message) => {
        await bot.reply(message, 'I heard a sample message.');
    });
}

Now you can also, optionally, use:

export default (controller) => {
    // ...
}

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[cooperka]

[not stale]

[benbrown]

I'll get this merged in to the next release.