update: stop autoupdate skipping no formula taps.
update: stop autoupdate skipping no formula taps.

This will be slightly slower if you have a bunch of non-formula (i.e.
command or cask) taps but it avoids the confusion of having Homebrew
saying it's updated when it only did so selectively.

Fixes #1946.

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