Updated KDE runtime to latest LTS

docs/deployment/linux-flatpak/org.opl.openPilotLog.yaml

@@ -1,6 +1,6 @@
 id: org.opl.openPilotLog
 runtime: org.kde.Platform
-runtime-version: '5.15'
+runtime-version: '5.15-21.08'
 sdk: org.kde.Sdk
 command: openPilotLog
 finish-args: