Update link to screenshot

org.kde.kmouth.appdata.xml

@@ -107,7 +107,7 @@
   <url type="homepage">https://www.kde.org/applications/utilities/kmouth/</url>
   <screenshots>
     <screenshot type="default">
-      <image>https://www.kde.org/images/screenshots/kmouth.png</image>
+      <image>https://cdn.kde.org/screenshots/kmouth/kmouth.png</image>
     </screenshot>
   </screenshots>
   <project_group>KDE</project_group>