fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-JINJA2-6150717
- https://snyk.io/vuln/SNYK-PYTHON-PYGMENTS-5750273
- https://snyk.io/vuln/SNYK-PYTHON-TORNADO-5537286
- https://snyk.io/vuln/SNYK-PYTHON-TORNADO-5840803
- https://snyk.io/vuln/SNYK-PYTHON-TORNADO-6041512

requirements.txt

@@ -1,14 +1,14 @@
 Click==8.1.3
 htmlmin==0.1.12
 jsmin==3.0.1
-Jinja2==3.1.2
+Jinja2==3.1.3
 livereload==2.6.3
 Markdown==3.3.7
 MarkupSafe==2.1.1
 mkdocs==1.4.2
 mkdocs-minify-plugin==0.6.2
 mkdocs-material==9.0.3
 pep562==1.1
-Pygments==2.14.0
+Pygments==2.15.0
 six==1.16.0
-tornado==6.2
+tornado==6.3.3