Use ES6 `import` instead of `required`

[huan]

In the Wechaty community, we are using ESM now.

Please always use import to load the module instead of required.

https://github.com/wechaty/wechaty-puppet-walnut/blob/5d1e70d8128d9183592bf273a4765341e55de862/src/utils/getAccessToken.ts#L9-L10

And please rename the getAccessToken.ts to get-access-token.ts because we need to follow the file name convention of our community.