devel/py-Jinja2: fix build of the slave port devel/py-Jinja2-doc

The slave port requires a version of the dependecy
textproc/py-pallets-sphinx-themes >= 2.0.2.

Poudriere log: https://gist.github.com/nivit/01f2cb9a413b7c97c48435b9cf923df3
Reported by: pkg-fallout