Set HOMEBREW_BOTTLE_DEFAULT_DOMAIN based on operating system

Resolve formulae in `brew cleanup`.

README: remove DomT4.

I resign from Homebrew with immediate effect.

Goodbye Homebrew.

docs/Maintainer-Guidelines: retire lead maintainer position in Febuary.

Bump parser from 2.5.1.0 to 2.5.1.2 in /Library/Homebrew/test

Merge pull request #4881 from Homebrew/dependabot/bundler/Library/Homebrew/test/rspec-expectations-3.8.1

Bump rspec-expectations from 3.8.0 to 3.8.1 in /Library/Homebrew/test

Bump commonmarker from 0.17.12 to 0.17.13 in /docs

Bump docile from 1.3.0 to 1.3.1 in /Library/Homebrew/test

Merge pull request #4883 from Homebrew/dependabot/bundler/Library/Homebrew/test/ruby-progressbar-1.10.0

Bump ruby-progressbar from 1.9.0 to 1.10.0 in /Library/Homebrew/test

Bumps [ruby-progressbar](https://github.com/jfelchner/ruby-progressbar) from 1.9.0 to 1.10.0.
- [Release notes](https://github.com/jfelchner/ruby-progressbar/releases)
- [Changelog](https://github.com/jfelchner/ruby-progressbar/blob/master/CHANGELOG.md)
- [Commits](https://github.com/jfelchner/ruby-progressbar/compare/releases/v1.9.0...releases/v1.10.0

)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [parser](https://github.com/whitequark/parser) from 2.5.1.0 to 2.5.1.2.
- [Release notes](https://github.com/whitequark/parser/releases)
- [Changelog](https://github.com/whitequark/parser/blob/master/CHANGELOG.md)
- [Commits](https://github.com/whitequark/parser/compare/v2.5.1.0...v2.5.1.2

)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [rspec-expectations](https://github.com/rspec/rspec-expectations) from 3.8.0 to 3.8.1.
- [Release notes](https://github.com/rspec/rspec-expectations/releases)
- [Changelog](https://github.com/rspec/rspec-expectations/blob/master/Changelog.md)
- [Commits](https://github.com/rspec/rspec-expectations/compare/v3.8.0...v3.8.1

)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [commonmarker](https://github.com/gjtorikian/commonmarker) from 0.17.12 to 0.17.13.
- [Release notes](https://github.com/gjtorikian/commonmarker/releases)
- [Commits](https://github.com/gjtorikian/commonmarker/compare/v0.17.12...v0.17.13

)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [docile](https://github.com/ms-ati/docile) from 1.3.0 to 1.3.1.
- [Release notes](https://github.com/ms-ati/docile/releases)
- [Changelog](https://github.com/ms-ati/docile/blob/master/HISTORY.md)
- [Commits](https://github.com/ms-ati/docile/compare/v1.3.0...v1.3.1

)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Elide prefix "/usr/local" in bottle block

brew test-bot --ci-upload is run on a Linux machine.
The macOS bottles have a prefix of "/usr/local".
The default prefix on Linux is /home/linuxbrew/.linuxbrew.
Elide prefix "/usr/local" in the bottle block, even it does not match
the default prefix. Ditto for cellar.

Bump octokit from 4.11.0 to 4.12.0 in /docs

Add Homebrew::DEFAULT_PREFIX for Linux

Bumps [octokit](https://github.com/octokit/octokit.rb) from 4.11.0 to 4.12.0.
- [Release notes](https://github.com/octokit/octokit.rb/releases)
- [Changelog](https://github.com/octokit/octokit.rb/blob/master/RELEASE.md)
- [Commits](https://github.com/octokit/octokit.rb/compare/v4.11.0...v4.12.0

)

Signed-off-by: dependabot[bot] <support@dependabot.com>

The default prefix is /usr/local on macOS
and /home/linuxbrew/.linuxbrew on Linux.

Don’t add error when changing checksum to `:no_check`.

cmd/update: follow GitHub API redirects.

Cask: show previous verison in cask upgrade

Fixes #4867

Determine remote_url using git config

Bump github-pages from 191 to 192 in /docs

docs/Maintainer-Guidelines: add more guidelines.

Bumps [github-pages](https://github.com/github/pages-gem) from 191 to 192.
- [Release notes](https://github.com/github/pages-gem/releases)
- [Commits](https://github.com/github/pages-gem/compare/v191...v192

)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Cask: fixes for quarantining