v1.8.4: 🪜 Unsupported updates != outdated

Changes

• ⚠️ Add a temporary warning about macOS Monterey (#427) @chris-araman
• 🐛 Print warnings and errors to stderr (#427) @chris-araman
• 🐛 Use POSIX-compliant tail syntax (#418) @jlec
• 🍺 Include macOS 12 Monterey when bottling (#424) @chris-araman
• ⬆️ PromiseKit (6.16.1) (#425) @chris-araman
• ⬆️ danger (8.4.1) (#423) @dependabot
• 🐛 Don't consider an app outdated if the update can't be installed on the current OS (#422) @phatblat
• ⬆️ Danger (8.4.0) (#419) @dependabot
• ⬆️ PromiseKit (6.16.0) (#415) @chris-araman
• 🍺 Homebrew formula for 1.8.3 (#411) @phatblat