fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-CERTIFI-3164749
- https://snyk.io/vuln/SNYK-PYTHON-FLASK-5490129
- https://snyk.io/vuln/SNYK-PYTHON-GUNICORN-7856105
- https://snyk.io/vuln/SNYK-PYTHON-IDNA-6597975
- https://snyk.io/vuln/SNYK-PYTHON-JINJA2-6150717
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-6043904
- https://snyk.io/vuln/SNYK-PYTHON-REQUESTS-5595532
- https://snyk.io/vuln/SNYK-PYTHON-SETUPTOOLS-3180412
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-5926907
- https://snyk.io/vuln/SNYK-PYTHON-WERKZEUG-3319935
- https://snyk.io/vuln/SNYK-PYTHON-WERKZEUG-3319936

requirements.txt

@@ -1,17 +1,19 @@
 autopep8==1.6.0
-certifi==2020.6.20
+certifi==2022.12.7
 chardet==3.0.4
 click==7.1.2
-Flask==1.1.4
-gunicorn==20.1.0
-idna==2.10
+Flask==2.2.5
+gunicorn==21.2.0
+idna==3.7
 itsdangerous==1.1.0
-Jinja2==2.11.3
+Jinja2==3.1.3
 MarkupSafe==2.0.1
 pycodestyle==2.8.0
 python-dotenv==0.14.0
-requests==2.28.1
+requests==2.31.0
 toml==0.10.2
-urllib3==1.26.12
-Werkzeug==1.0.1
+urllib3==1.26.17
+Werkzeug==2.2.3
 colorthief==0.2.1
+pillow>=10.0.0 # not directly required, pinned by Snyk to avoid a vulnerability
+setuptools>=65.5.1 # not directly required, pinned by Snyk to avoid a vulnerability