Fixed PHPUnit doc URL

Any links to `www.phpunit.de` now redirects to the front page. Stripping `www.` off fixes the issue.
minor #623 Fixed PHPUnit doc URL (gnugat)

This PR was submitted for the 2.3-dev branch but it was merged into the 2.3 branch instead (closes #623).

Discussion
----------

Fixed PHPUnit doc URL

Any links to `www.phpunit.de` now redirects to the front page. Stripping `www.` off fixes the issue.

Commits
-------

e958959 Fixed PHPUnit doc URL