AppImage: Use new build tool with runtime2 support (#3586)

Closes #3055

dist/linux/appimage/build.sh

@@ -114,7 +114,7 @@ ln -s usr/share/applications/org.cryptomator.Cryptomator.desktop Cryptomator.App
 ln -s bin/cryptomator.sh Cryptomator.AppDir/AppRun
 
 # load AppImageTool
-curl -L https://github.com/AppImage/AppImageKit/releases/download/13/appimagetool-${CPU_ARCH}.AppImage -o /tmp/appimagetool.AppImage
+curl -L https://github.com/AppImage/appimagetool/releases/download/continuous/appimagetool-${CPU_ARCH}.AppImage -o /tmp/appimagetool.AppImage
 chmod +x /tmp/appimagetool.AppImage
 
 # create AppImage