chore: avoid non-unicode characters

Author: jo-mueller

pre_build.py

@@ -157,8 +157,8 @@ def build_footer():
     year = datetime.now().year
     footer_content = f"""
 <div>
-    Copyright © 2020-{year}
-    <a href="https://www.openmicroscopy.org/"><abbr title="Open Microscopy Environment">OME</abbr></a><sup>®</sup>.
+    Copyright &copy; 2020-{year}
+    <a href="https://www.openmicroscopy.org/"><abbr title="Open Microscopy Environment">OME</abbr></a><sup>&reg;</sup>.
     OME trademark rules apply.
 </div>
 """