move to heroku

See #1217, release log:

• 4662cb9 by @yegor256: 1217 heroku
• 30f6766 by @yegor256: 1217 netrc
• 344e4ad by @yegor256: 1217 up
• 2b5e30f by @yegor256: heroku
• dabeded by @renovate[bot]: Update dependency minitest to ...
• aa5609e by @renovate[bot]: Update dependency minitest to ...
• 792e5ec by @renovate[bot]: Update dependency minitest to ...
• 1a2d8bd by @yegor256: #1211 extra tests
• e9fe65d by @renovate[bot]: Update codecov/codecov-action ...

Released by Rultor 2.0-SNAPSHOT, see build log