Added Cask tower2

[edrozenberg]

In reference to issue #5874 which says ok to add tower2.

Since Tower.app v3 has switched to subscriptions (booh!), adding this tower2 alternate version cask.

This is simply a copy of an older revision of the tower.rb cask from the homebrew-cask project, with cask name changed from ‘tower’ to ‘tower2’.

After making all changes to the cask:

• brew cask audit --download {{cask_file}} is error-free.
  brew cask audit --download https://raw.githubusercontent.com/edrozenberg/homebrew-cask-versions/master/Casks/tower2.rb
audit for tower2: passed
• brew cask style --fix {{cask_file}} reports no offenses.
  brew cask style --fix tower2
1 file inspected, no offenses detected
• The commit message includes the cask’s name and version.

Additionally, if adding a new cask:

• Named the cask according to the token reference.
  tower2
• brew cask install {{cask_file}} worked successfully.

==> Satisfying dependencies
==> Downloading https://fournova-app-updates.s3.amazonaws.com/apps/tower2-mac/35
Already downloaded: /Users/eduardr/Library/Caches/Homebrew/Cask/tower2--2.6.6-359,b84d867f.zip
==> Verifying checksum for Cask tower2
==> Installing Cask tower2
==> Moving App 'Tower.app' to '/Applications/Tower.app'.
==> Linking Binary 'gittower' to '/usr/local/bin/gittower'.
tower2 was successfully installed!

• brew cask uninstall {{cask_file}} worked successfully.

==> Uninstalling Cask tower2
==> Backing App 'Tower.app' up to '/usr/local/Caskroom/tower2/2.6.6-359,b84d867f
==> Removing App '/Applications/Tower.app'.
==> Unlinking Binary '/usr/local/bin/gittower'.
==> Purging files for version 2.6.6-359,b84d867f of Cask tower2

• Checked there are no open pull requests for the same cask.
• Checked the cask was not already refused in closed issues.
• Checked the cask is submitted to the correct repo.

[justrhysism]

Yeah I'm sticking my bought licence for as long as I can now. The Tower subscription is absurdly expensive.