Conditional nits in 21 Casks

Principally the use of inclusive operators, which is to me more readable, especially as the included release may be present in the URL as in https://github.com/rolandwalker/homebrew-cask/commit/3c893b6770904014f749f4c438f9735a4b82eea7#diff-f90ed069be50cb56a7c661efd3236289L6 .

Also abstracts a few repeated elements out of conditionals.