fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-TORNADO-7217828
- https://snyk.io/vuln/SNYK-PYTHON-TORNADO-7217829

requirements.txt

@@ -12,5 +12,5 @@ psutil>=5.6.5; sys_platform == 'win32'
 python-dateutil
 requests
 SQLAlchemy>=1.1
-tornado>=5.1
+tornado>=6.4.1
 traitlets>=4.3.2