fix: shards/requirements.txt to reduce vulnerabilities (#3457)

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-SQLALCHEMY-590109

shards/requirements.txt

@@ -29,7 +29,7 @@ requests==2.22.0
 requests-oauthlib==1.2.0
 rsa==4.1
 six==1.12.0
-SQLAlchemy==1.3.5
+SQLAlchemy==1.3.19
 ujson==2.0.1
 urllib3==1.25.8
 jaeger-client>=3.4.0