GIT_SILENT Update Appstream for new release

(cherry picked from commit 9ff62019)

ktorrent/org.kde.ktorrent.appdata.xml

@@ -798,10 +798,10 @@
     <binary>ktorrent</binary>
   </provides>
   <releases>
+    <release version="20.12.0" date="2020-12-10"/>
     <release version="5.2.0" date="2020-06-06"/>
     <release version="5.1.2" date="2019-09-01"/>
     <release version="5.1.1" date="2018-08-28"/>
-    <release version="5.1.0" date="2017-08-31"/>
   </releases>
   <content_rating type="oars-1.1"/>
 </component>