fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-571013
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-571014

requirements.txt

@@ -1,5 +1,5 @@
 croniter==0.3.31
-Django==3.0.4
+Django==3.0.7
 django-compressor==2.4
 psycopg2==2.8.4
 pytz==2020.1