Add frozen_string_literal to all files.

Library/Homebrew/Gemfile

Library/Homebrew/PATH.rb

Library/Homebrew/brew.rb

Library/Homebrew/build.rb

Library/Homebrew/build_environment.rb

Library/Homebrew/build_options.rb

Library/Homebrew/cache_store.rb

Library/Homebrew/cask/all.rb

Library/Homebrew/cask/artifact.rb

Library/Homebrew/cask/artifact/abstract_artifact.rb

Library/Homebrew/cask/artifact/abstract_flight_block.rb

Library/Homebrew/cask/artifact/abstract_uninstall.rb

Library/Homebrew/cask/artifact/app.rb

Library/Homebrew/cask/artifact/artifact.rb

Library/Homebrew/cask/artifact/audio_unit_plugin.rb

Library/Homebrew/cask/artifact/binary.rb

Library/Homebrew/cask/artifact/colorpicker.rb

Library/Homebrew/cask/artifact/dictionary.rb

Library/Homebrew/cask/artifact/font.rb

Library/Homebrew/cask/artifact/input_method.rb