fix: cvat/requirements/base.txt to reduce vulnerabilities (#3063)

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-1090584
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-1090586
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-1090587
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-1090588

cvat/requirements/base.txt

@@ -6,7 +6,7 @@ django-cacheops==5.0.1
 django-compressor==2.4
 django-rq==2.3.2
 EasyProcess==0.3
-Pillow==8.1.2
+Pillow==8.2.0
 numpy==1.19.5
 python-ldap==3.3.1
 pytz==2020.1