bump-cask-pr: avoid replacing sha256 twice on multilang cask
bump-cask-pr: avoid replacing sha256 twice on multilang cask

this script always get `inreplace failed` on cask like firefox because the
default sha256 is replaced twice

nandub/brew,MikeMcQuaid/brew,JCount/brew,Homebrew/brew,nandub/brew,nandub/brew,Homebrew/brew,MikeMcQuaid/brew,Homebrew/brew,MikeMcQuaid/brew,Homebrew/brew,MikeMcQuaid/brew,JCount/brew,JCount/brew,JCount/brew,nandub/brew