fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-1533435

requirements.txt

@@ -92,7 +92,7 @@ soupsieve==1.9.5          # via -r requirements.in, beautifulsoup4
 typing-extensions==3.7.4.3  # via apache-beam
 typing==3.7.4.3           # via apache-beam, typing-extensions
 uritemplate==3.0.1        # via google-api-python-client
-urllib3==1.25.11          # via elasticsearch, requests
+urllib3==1.26.5          # via elasticsearch, requests
 webapp2==3.0.0b1          # via -r requirements.in
 webencodings==0.5.1       # via -r requirements.in, bleach, html5lib
 webob==1.8.6              # via webapp2