formula.rb: Move cache dir creation to fetch
formula.rb: Move cache dir creation to fetch

So that the cache directory will get created if the user runs `brew fetch`
instead of `brew install` as the first command.

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