Fix undefined method 'all' for class Cask::Cask in deps command

[middagj]

Similar to 92b5c0c but then for cmd/deps.rb

cmd/deps: require cask/cask

Currently brew deps fails with the following error:

$ brew deps
Error: undefined method 'all' for class Cask::Cask
/opt/homebrew/Library/Homebrew/cmd/deps.rb:195:in 'block in Homebrew::Cmd::Deps#run'
/opt/homebrew/Library/Homebrew/simulate_system.rb:40:in 'Homebrew::SimulateSystem.with'
/opt/homebrew/Library/Homebrew/cmd/deps.rb:125:in 'Homebrew::Cmd::Deps#run'
/opt/homebrew/Library/Homebrew/brew.rb:142:in '<main>'
Please report this issue:
  https://docs.brew.sh/Troubleshooting

I did not add a test, since in my opinion this should already be catch.

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[MikeMcQuaid]

Thanks!