gitignore: fix Git 2.7.0 behaviour.
gitignore: fix Git 2.7.0 behaviour.

Closes Homebrew/homebrew#47710.

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