use on_mojave block on ableton-live-intro

[hyuraku]

Important: Do not tick a checkbox if you haven’t performed its action. Honesty is indispensable for a smooth review process.

In the following questions <cask> is the token of the cask you're submitting.

After making all changes to a cask, verify:

• The submission is for a stable version or documented exception.
• brew audit --cask --online <cask> is error-free.
• brew style --fix <cask> reports no offenses.

repair for Migrate all casks to use on_{macos_version} blocks instead of if MacOS.version conditionals on Homebrew/brew#13794

Additionally, if adding a new cask:

• Named the cask according to the token reference.
• Checked the cask was not already refused.
• Checked the cask is submitted to the correct repo.
• brew audit --new-cask <cask> worked successfully.
• brew install --cask <cask> worked successfully.
• brew uninstall --cask <cask> worked successfully.