language/python: allow python@3.7 to be used for virtualenvs
language/python: allow python@3.7 to be used for virtualenvs

sjackman/homebrew,vitorgalvao/brew,claui/brew,mahori/brew,JCount/brew,MikeMcQuaid/brew,JCount/brew,mahori/brew,MikeMcQuaid/brew,sjackman/homebrew,nandub/brew,sjackman/homebrew,Homebrew/brew,vitorgalvao/brew,Homebrew/brew,vitorgalvao/brew,mahori/brew,nandub/brew,Homebrew/brew,claui/brew,konqui/brew,konqui/brew,EricFromCanada/brew,EricFromCanada/brew,claui/brew,mahori/brew,konqui/brew,JCount/brew,EricFromCanada/brew,nandub/brew,reitermarkus/brew,EricFromCanada/brew,reitermarkus/brew,konqui/brew,reitermarkus/brew,sjackman/homebrew,MikeMcQuaid/brew,claui/brew,vitorgalvao/brew,nandub/brew,reitermarkus/brew,Homebrew/brew,JCount/brew,MikeMcQuaid/brew