using the `access_token` query parameter is deprecated

I just received a notification email from GitHub after using this package to copy labels. It might be good to disable support for this method of auth and remove from documentation.

> Hi @arpieb,
>
> On March 11th, 2021 at 17:10 (UTC) your personal access token (---) using Copy-GitHub-Labels octokit.js/15.18.3 Node.js/15.8.0 (macOS Mojave; x64) was used as part of a query parameter to access an endpoint through the GitHub API:
>
> https://api.github.com/repositories/---/labels
>
> Please use the Authorization HTTP header instead, as using the `access_token` query parameter is deprecated. If this token is being used by an app you don't have control over, be aware that it may stop working as a result of this deprecation.
>
> Depending on your API usage, we'll be sending you this email reminder on a monthly basis for each token and User-Agent used in API calls made on your behalf.
> Just one URL that was accessed with a token and User-Agent combination will be listed in the email reminder, not all.
>
> Visit https://developer.github.com/changes/2020-02-10-deprecating-auth-through-query-param for more information about suggested workarounds and removal dates.
>
> Thanks,
> The GitHub Team
>