Create pdf-expert-beta.rb (#8308)
Create pdf-expert-beta.rb (#8308)

Add cask for Beta versions of PDF Expert.
rogeriopradoj/homebrew-versions,mahori/homebrew-cask-versions,pkq/homebrew-versions,lantrix/homebrew-versions,rogeriopradoj/homebrew-versions,caskroom/homebrew-versions,pkq/homebrew-versions,caskroom/homebrew-versions,lantrix/homebrew-versions,404NetworkError/homebrew-versions,404NetworkError/homebrew-versions