Update python 'requests' lib min version

Gerold103 · web-flow · commit a3069d4a0e8b · 2019-04-12T15:49:50.000+03:00
GitHub said, that the previous was vulnerable for network sniffing.
diff --git a/requirements.txt b/requirements.txt
@@ -1,3 +1,3 @@
 bottle==0.12.13
-requests==2.19.1
+requests>=2.20.0
 gunicorn==19.9.0
