Fix Style/GuardClause.

Library/.rubocop_todo.yml

Library/Homebrew/cmd/install.rb

Library/Homebrew/cmd/update-report.rb

Library/Homebrew/dependency_collector.rb

Library/Homebrew/dev-cmd/audit.rb

Library/Homebrew/dev-cmd/pull.rb

Library/Homebrew/dev-cmd/test-bot.rb

Library/Homebrew/download_strategy.rb

Library/Homebrew/extend/ARGV.rb

Library/Homebrew/extend/ENV/shared.rb

Library/Homebrew/extend/ENV/std.rb

Library/Homebrew/extend/ENV/super.rb

Library/Homebrew/extend/fileutils.rb

Library/Homebrew/extend/os/mac/extend/ENV/std.rb

Library/Homebrew/extend/os/mac/formula_cellar_checks.rb

Library/Homebrew/extend/os/mac/utils/bottles.rb

Library/Homebrew/extend/string.rb

Library/Homebrew/formula.rb

Library/Homebrew/formula_installer.rb

Library/Homebrew/formula_lock.rb