Fix macOS feed title meta-click behavior

[kemayo]

Changes proposed in this pull request:

• On macOS, command-clicking the feed item's title should open the URL in a new tab, just as ctrl-clicking them on another OS would

How to test the feature manually:

1. Using macOS, command-click the link in a feed item's title
2. Using another OS, verify that this hasn't interfered with ctrl-clicking the feed item's title

Pull request checklist:

• clear commit messages
• code manually tested
• unit tests written (optional if too hard)
  -- Pure JS change, not unit-testable without major additions to the project
• documentation updated
  -- No documentation affected, but I did update the relevant comment in the JS file...

[Alkarex]

Welcome and thanks!