Bump jinja2 from 2.11.3 to 3.0.1 in /blockdiag

Bumps [jinja2](https://github.com/pallets/jinja) from 2.11.3 to 3.0.1.
- [Release notes](https://github.com/pallets/jinja/releases)
- [Changelog](https://github.com/pallets/jinja/blob/main/CHANGES.rst)
- [Commits](pallets/jinja@2.11.3...3.0.1)

Signed-off-by: dependabot[bot] <support@github.com>

blockdiag/requirements.txt

@@ -5,7 +5,7 @@ Flask==1.1.2
 funcparserlib==0.3.6
 gunicorn==20.1.0
 itsdangerous==1.1.0
-Jinja2==2.11.3
+Jinja2==3.0.1
 MarkupSafe==1.1.1
 nwdiag==2.0.0
 Pillow==8.2.0