Backport updated requirements.txt to 5.5

Author: TimWolla

requirements.txt

@@ -2,5 +2,5 @@ Markdown==3.3.7
 mike==1.1.2
 mkdocs-git-revision-date-plugin==0.3.2
 mkdocs-macros-plugin==0.7.0 
-mkdocs-material==8.2.14
-mkdocs==1.3.0
+mkdocs-material==9.0.6
+mkdocs==1.4.2