fix: avoid non-unicode characters

Author: jo-mueller

pre_build.py

@@ -162,8 +162,8 @@ 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>
     """