Bump down urllib3 to 1.25.11 to fix requests package conflict

Author: Anirudh Goel

requirements.txt

@@ -62,7 +62,7 @@ stripe==2.56.0
 toml==0.10.2
 traitlets==4.3.3
 typed-ast==1.4.3
-urllib3==1.26.5
+urllib3==1.25.11
 wcwidth==0.2.5
 Werkzeug==0.15.5
 wrapt==1.12.1