fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-FLASKCORS-6670412

requirements.txt

@@ -23,7 +23,7 @@ eventlet==0.30.2
 flasgger==0.9.5
 Flask==1.1.2
 Flask-BabelEx==0.9.4
-Flask-Cors==3.0.10
+Flask-Cors==4.0.1
 Flask-Login==0.5.0
 Flask-Mail==0.9.1
 Flask-Migrate==2.5.3