Update dependency pytz to v2020.5

Author: renovate-bot

requirements.txt

@@ -17,7 +17,7 @@ pyasn1==0.4.8
 pyasn1-modules==0.2.8
 pycparser==2.20
 python-resize-image==1.1.19
-pytz==2020.1
+pytz==2020.5
 requests==2.24.0
 rsa==4.6
 six==1.15.0