fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-CRYPTOGRAPHY-6092044

requirements.txt

@@ -37,7 +37,7 @@ xlrd>=1.0.0
 pdfkit==0.6.1
 Pillow==8.0.1  # required by django-imagekit
 psycopg2-binary==2.8.6
-cryptography==3.2.1
+cryptography==41.0.6
 python-dateutil==2.8.1
 python-nmap==0.6.1
 pytz==2020.4