Merge pull request #4310 from commitay/remove-checkpoint

Library/Homebrew/cask/lib/hbc/audit.rb

Library/Homebrew/cask/lib/hbc/cli.rb

.../Homebrew/cask/lib/hbc/cli/internal_appcast_checkpoint.rb

...omebrew/cask/lib/hbc/cli/internal_audit_modified_casks.rb

Library/Homebrew/cask/lib/hbc/dsl/appcast.rb

Library/Homebrew/manpages/brew-cask.1.md

Library/Homebrew/test/cask/audit_spec.rb

Library/Homebrew/test/cask/dsl/appcast_spec.rb

.../cask/Casks/appcast-checkpoint-sha256-for-empty-string.rb

...support/fixtures/cask/Casks/appcast-invalid-checkpoint.rb

...support/fixtures/cask/Casks/appcast-missing-checkpoint.rb

...st/support/fixtures/cask/Casks/appcast-with-checkpoint.rb

...w/test/support/fixtures/cask/Casks/github-with-appcast.rb

...t/fixtures/cask/Casks/invalid/invalid-appcast-multiple.rb

...upport/fixtures/cask/Casks/invalid/invalid-appcast-url.rb

...w/test/support/fixtures/cask/Casks/latest-with-appcast.rb

...t/support/fixtures/cask/Casks/sourceforge-with-appcast.rb

...Homebrew/test/support/fixtures/cask/Casks/with-appcast.rb

manpages/brew-cask.1