[KdePlasma-Addons/POTD/NOAA] Fixed RegEx string of landing page

Summary: 'Image of the day' has a new landing page everyday. This patch fixes the RegEx string that fetches the web address of the landing page.

Test Plan: All plugins should work as usual.

Reviewers: davidedmundson, ngraham

Reviewed By: davidedmundson, ngraham

Subscribers: ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D18232