[fix] #817 fix build.sh in ci/appimage to build inside a docker container

See https://appimage-builder.readthedocs.io/en/latest/intro/install.html#install-in-a-docker-container

ci/appimage/build.sh

 #!/bin/bash
-./linuxdeploy-x86_64.AppImage --appdir AppDir -i sakia.png -d sakia.desktop --plugin python --output appimage --custom-apprun sakia.sh
+#./linuxdeploy-x86_64.AppImage --appdir AppDir -i sakia.png -d sakia.desktop --plugin python --output appimage --custom-apprun sakia.sh
+# workaround to run inside a docker container
+./linuxdeploy-x86_64.AppImage --appimage-extract
+mv squashfs-root linuxdeploy-x86_64.AppDir
+./linuxdeploy-x86_64.AppDir/AppRun --appdir AppDir  -i sakia.png -d sakia.desktop --plugin python --output appimage --custom-apprun sakia.sh