Add `upgrade` to the zsh completion script
Add `upgrade` to the zsh completion script

Closes Homebrew/homebrew#7923.

Signed-off-by: Jack Nagel <43386ce32af96f5c56f2a88e458cb94cebee3751@gmail.com>

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