Make the git download strategy default to :branch => "master"
Make the git download strategy default to :branch => "master"

Fixes Homebrew/homebrew#33437.

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