Update matplotlib from 1.4.0 to 3.9.1.post1

Author: pyup-bot

requirements.txt

@@ -24,7 +24,7 @@ libmodernize==0.5
 markdown==2.6.2
 markdown2==2.2.1
 markupsafe
-matplotlib==1.4.0
+matplotlib==3.9.1.post1
 mccabe==0.4.0
 midiutil
 mpl_toolkits