Update appdata with new version

Author: grulja

org.flatpak.qtdemo.appdata.xml

@@ -15,6 +15,7 @@
     <p xml:lang="en-GB">The application demonstrates the use of portals, showing how it is possible to securely access host functions like file choosers, notifications and screenshots. To do this, it uses the built-in support provided by the Qt toolkit. Similar support is also available for GTK.</p>
   </description>
   <releases>
+    <release version="1.1.3" date="2018-10-22"/>
     <release version="1.1.2" date="2018-05-18"/>
     <release version="1.1.1" date="2018-05-18"/>
     <release version="1.1.0" date="2018-05-14"/>