Replace MIT license with AGPL-3.0-only.  Suffix "-only" here is
very important: redistribution is allowed _only_ under Version 3 of the
License -- see new boilerplate at the top of source file
copy-commit-reference.user.js, which I've taken from SPDX website.[1]

The actual text of the License was taken from choosealicense.com.[2]

See also "Why the Affero GPL" on the GNU website.[3]

[1] section "Standard License Header" on the page
    https://spdx.org/licenses/AGPL-3.0-only.html
[2] https://choosealicense.com/licenses/agpl-3.0/
[3] https://www.gnu.org/licenses/why-affero-gpl.html