Remove unnecessary nil check
Remove unnecessary nil check

The backticks will either return a string or raise an exception, so
`executable` cannot be nil.

Linuxbrew/brew,tonyg/homebrew,bfontaine/brew,maxim-belkin/brew,gregory-nisbet/brew,EricFromCanada/brew,vitorgalvao/brew,zmwangx/brew,gregory-nisbet/brew,alyssais/brew,nandub/brew,reitermarkus/brew,palxex/brew,gordonmcshane/homebrew,tonyg/homebrew,amar-laksh/brew_sudo,rwhogg/brew,JCount/brew,mistydemeo/homebrew,rwhogg/brew,toonetown/homebrew,nandub/brew,aw1621107/brew,mahori/brew,EricFromCanada/brew,ilovezfs/brew,pseudocody/brew,DomT4/brew,staticfloat/brew,reitermarkus/brew,Homebrew/brew,nandub/brew,maxim-belkin/brew,toonetown/homebrew,mgrimes/brew,MikeMcQuaid/brew,aw1621107/brew,mgrimes/brew,Homebrew/brew,Homebrew/brew,vitorgalvao/brew,amar-laksh/brew_sudo,Linuxbrew/brew,MikeMcQuaid/brew,muellermartin/dist,JCount/brew,jmsundar/brew,alyssais/brew,mgrimes/brew,hanxue/linuxbrew,jmsundar/brew,reelsense/brew,claui/brew,DomT4/brew,bfontaine/brew,rwhogg/brew,mistydemeo/homebrew,pseudocody/brew,Homebrew/brew,reelsense/brew,palxex/brew,AnastasiaSulyagina/brew,vitorgalvao/brew,claui/brew,muellermartin/dist,sjackman/homebrew,mahori/brew,reitermarkus/brew,toonetown/homebrew,gordonmcshane/homebrew,gordonmcshane/homebrew,reelsense/brew,alyssais/brew,MikeMcQuaid/brew,DomT4/brew,EricFromCanada/brew,maxim-belkin/brew,tonyg/homebrew,sjackman/homebrew,staticfloat/brew,sjackman/homebrew,claui/brew,mistydemeo/homebrew,MikeMcQuaid/brew,reitermarkus/brew,nandub/brew,pseudocody/brew,ilovezfs/brew,amar-laksh/brew_sudo,aw1621107/brew,hanxue/linuxbrew,JCount/brew,claui/brew,gregory-nisbet/brew,konqui/brew,bfontaine/brew,ilovezfs/brew,mahori/brew,EricFromCanada/brew,palxex/brew,konqui/brew,AnastasiaSulyagina/brew,vitorgalvao/brew,konqui/brew,Linuxbrew/brew,sjackman/homebrew,AnastasiaSulyagina/brew,muellermartin/dist,hanxue/linuxbrew,zmwangx/brew,konqui/brew,staticfloat/brew,DomT4/brew,jmsundar/brew,Linuxbrew/brew,mahori/brew,JCount/brew,zmwangx/brew