accessibility/orca: Fix pkg-descr ending with a URL
A URL ending a sentence, with a full stop after it, causes pain
for renderers such as freshports.org and other clients that may hyperlink
Since the same URL is just below it in the pkg-descr WWW URL, amend
the sentence to point to it instead.
Reported by: Graham Perrin <grahamperrin gmail com>
Approved by: portmgr (blanket: just fix it)