fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-LXML-1088006

Author: snyk-bot

requirements.txt

@@ -4,7 +4,7 @@ mod-wsgi==4.6.8
 django>=2.2.13
 
 
-lxml==4.6.2
+lxml==4.6.3
 urllib3>=1.25.9
 suds-py3==1.3.4.0
 biopython==1.72