docs: handle deprecation warning wrt. emojis (#202)

### Summary of Changes

Update Material for Mkdocs configuration to handle a deprecation
warning.

Author: lars-reimann

mkdocs.yml

@@ -96,18 +96,18 @@ markdown_extensions:
           class: mermaid
           format: !!python/name:pymdownx.superfences.fence_code_format
 
-          # Footnotes
+  # Footnotes
   - footnotes
 
   # Keys
   - pymdownx.keys
 
   # Icons & emojis
   - pymdownx.emoji:
-      emoji_index: !!python/name:materialx.emoji.twemoji
-      emoji_generator: !!python/name:materialx.emoji.to_svg
+      emoji_index: !!python/name:material.extensions.emoji.twemoji
+      emoji_generator: !!python/name:material.extensions.emoji.to_svg
 
-      # Images
+  # Images
   - attr_list
   - md_in_html