ruby.sh: fix version check.
ruby.sh: fix version check.

- Rather than checking for the absence of a failure check for an actual success in the check
- Fix the check to work on Ruby 1.9 (where `RUBY_VERSION.to_s.dup` is required to avoid modifying a frozen string).

sjackman/homebrew,JCount/brew,EricFromCanada/brew,mahori/brew,MikeMcQuaid/brew,mgrimes/brew,konqui/brew,Linuxbrew/brew,DomT4/brew,sjackman/homebrew,claui/brew,claui/brew,Linuxbrew/brew,reelsense/brew,claui/brew,nandub/brew,MikeMcQuaid/brew,MikeMcQuaid/brew,Homebrew/brew,EricFromCanada/brew,alyssais/brew,Linuxbrew/brew,reitermarkus/brew,MikeMcQuaid/brew,alyssais/brew,reelsense/brew,JCount/brew,DomT4/brew,Homebrew/brew,sjackman/homebrew,sjackman/homebrew,mahori/brew,hanxue/linuxbrew,konqui/brew,konqui/brew,maxim-belkin/brew,konqui/brew,reitermarkus/brew,mgrimes/brew,maxim-belkin/brew,reitermarkus/brew,mahori/brew,Homebrew/brew,JCount/brew,nandub/brew,vitorgalvao/brew,maxim-belkin/brew,reitermarkus/brew,hanxue/linuxbrew,EricFromCanada/brew,EricFromCanada/brew,ilovezfs/brew,ilovezfs/brew,reelsense/brew,DomT4/brew,Linuxbrew/brew,mahori/brew,nandub/brew,vitorgalvao/brew,mgrimes/brew,vitorgalvao/brew,Homebrew/brew,alyssais/brew,nandub/brew,JCount/brew,claui/brew,vitorgalvao/brew,hanxue/linuxbrew,ilovezfs/brew,DomT4/brew