libical: updated homepage

[bwagner]

All Submissions:

• [ ] Have you followed the guidelines in our Contributing document?
• [ ] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

You can erase any parts of this template not applicable to your Pull Request.

New Formulae Submissions:

• [ ] Does your submission pass brew audit --strict --online <formula> (where <formula> is the name of the formula you're submitting)?
• [ ] Have you built your formula locally prior to submission with brew install <formula>?

  Changes to Homebrew's Core:

• [ ] Have you added an explanation of what your changes do and why you'd like us to include them?
• [ ] Have you written new tests for your core changes, as applicable? Here's an example if you'd like one.
• [ ] Have you successfully ran brew tests with your changes locally?

[apjanke]

Merged. Thank you for your contribution to Homebrew!