This PR adjusts the action so that it is no longer necessary to
explicitly specify the GitHub token to circumvent the API rate limit.
To this end, it simply passes the repository's GitHub token (available
via `${{ github.token }}`) as a default for the `github_token` action
input.
This is similar to how this is handled in, e.g.,
https://github.com/peter-evans/create-pull-request; specifically
[here](5354f85616/action.yml (L4-L6)).
Closes: #40
Because of build conflics (forgot to run `npm i` after pulling) I
deleted the `dist`folder to start fresh. Turns out that it still
contained the source maps from the very first commit. I removed the
argument to generate those a long time ago
