Setting upper version bound for urllib3

Since google-auth doesn't support urllib3>2.0 (googleapis/google-auth-library-python#1365), an upper version bound for urllib3 needs to be set. Otherwise the package is not installable, since the dependency to google-auth breaks.

Author: jsaalfeld

requirements.txt

@@ -9,4 +9,4 @@ websocket-client>=0.32.0,!=0.40.0,!=0.41.*,!=0.42.* # LGPLv2+
 requests # Apache-2.0
 requests-oauthlib # ISC
 oauthlib>=3.2.2 # BSD
-urllib3>=1.24.2  # MIT
+urllib3>=1.24.2,<2.0  # MIT