formula_installer.rb: Hotfix for head installs
formula_installer.rb: Hotfix for head installs

For now, don't strip `--HEAD` from `ARGV` prior to forking for install.
Currently this doesn't work because the formula object the installer is acting
on has its `prefix` set while under the influence of `--HEAD`. So, the
installer bails out when it sees that nothing is installed to `f.prefix`.

This is a hotfix for issue Homebrew/homebrew#8668 to allow formulae to keep building. A proper
fix should ensure that formula installers are operating on objects with
appropriately set `prefix` values.

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