Bumping Jinja2 to non-vulnerable version

* The previous version of Jinja2 was flagged as vulnerable,
  so this change bumps the version.
  https://github.com/advisories/GHSA-h75v-3vvj-5mfj



Change-Id: Iaea4457e6f8132e82faa21be3cda5011a2f1425a
Signed-off-by: Conor Kennedy <conor.kennedy@arm.com>