Fix deprecated macOS dependency syntax

[0xdevalias]

Summary

• Replace deprecated string-comparison depends_on macos: requirements with symbol requirements.
• Apply the fix to all four affected casks: deeper, istanbul, poke-gate, and wvw.

Fixes #1.

Validation

• git diff --check
• ruby -c for each changed cask
• Repo-wide search confirmed no remaining depends_on macos: ">= :..." requirements

brew style and brew audit were also attempted, but Homebrew rejected file-based validation from this workspace clone because it is not registered as a tap, and path arguments to brew audit are disabled.

References

• Homebrew Cask Cookbook: depends_on macos documents the symbol form for minimum macOS requirements and marks the older string-comparison form as deprecated.
• Homebrew/brew#22185: Align cask macOS dependencies introduced the migration to formula-style symbols for minimum macOS requirements.
• MacOSRequirement.parse emits the deprecation warning and maps ">= :version" to depends_on macos: :version.