bin/brew: whitelist http_proxy.
bin/brew: whitelist http_proxy.

Fixes #3494.

alyssais/brew,Linuxbrew/brew,pseudocody/brew,MikeMcQuaid/brew,JCount/brew,claui/brew,vitorgalvao/brew,aw1621107/brew,mahori/brew,vitorgalvao/brew,maxim-belkin/brew,Homebrew/brew,DomT4/brew,nandub/brew,vitorgalvao/brew,hanxue/linuxbrew,Linuxbrew/brew,Homebrew/brew,pseudocody/brew,aw1621107/brew,sjackman/homebrew,konqui/brew,mgrimes/brew,sjackman/homebrew,MikeMcQuaid/brew,konqui/brew,sjackman/homebrew,MikeMcQuaid/brew,vitorgalvao/brew,MikeMcQuaid/brew,reitermarkus/brew,konqui/brew,mgrimes/brew,JCount/brew,DomT4/brew,claui/brew,pseudocody/brew,EricFromCanada/brew,maxim-belkin/brew,DomT4/brew,ilovezfs/brew,mahori/brew,reitermarkus/brew,nandub/brew,alyssais/brew,EricFromCanada/brew,JCount/brew,nandub/brew,Homebrew/brew,reelsense/brew,Linuxbrew/brew,sjackman/homebrew,mahori/brew,reitermarkus/brew,claui/brew,ilovezfs/brew,hanxue/linuxbrew,reelsense/brew,reelsense/brew,aw1621107/brew,claui/brew,DomT4/brew,konqui/brew,EricFromCanada/brew,mahori/brew,Linuxbrew/brew,JCount/brew,mgrimes/brew,nandub/brew,ilovezfs/brew,Homebrew/brew,alyssais/brew,maxim-belkin/brew,EricFromCanada/brew,hanxue/linuxbrew,reitermarkus/brew