Update mkdocs dependencies

Author: mdmintz

mkdocs_build/requirements.txt

@@ -20,14 +20,14 @@ bleach==6.0.0
 lunr==0.6.2
 nltk==3.8.1
 tornado==6.2
-watchdog==2.3.0
+watchdog==2.3.1
 cairocffi==1.4.0
 cairosvg==2.6.0
 cssselect2==0.7.0
 tinycss2==1.2.1
 defusedxml==0.7.1
 mkdocs==1.4.2
-mkdocs-material==9.0.14
+mkdocs-material==9.0.15
 mkdocs-exclude-search==0.6.5
 mkdocs-simple-hooks==0.1.5
 mkdocs-material-extensions==1.1.1