📚 Fix image link on edge repo (#66)

Author: sinclairpaul

bookstack/.README.j2

@@ -64,4 +64,4 @@ If you are more interested in stable releases of our add-ons:
 [project-stage-shield]: https://img.shields.io/badge/project%20stage-experimental-yellow.svg
 [release-shield]: https://img.shields.io/badge/version-{{ version }}-blue.svg
 [release]: {{ repo }}/tree/{{ version }}
-[screenshot]: https://github.com/hassio-addons/addon-bookstack/raw/master/images/screenshot.png
+[screenshot]: https://github.com/hassio-addons/addon-bookstack/raw/main/images/screenshot.png