Fix filter_mathstuff integration test.

test/integration/targets/filter_mathstuff/runme.sh

@@ -11,7 +11,7 @@ source virtualenv.sh
 # Install Jinja < 2.10 since we want to test the fallback to Ansible's custom
 # unique filter. Jinja < 2.10 does not have do_unique so we will trigger the
 # fallback.
-pip install 'jinja2 < 2.10'
+pip install 'jinja2 < 2.10' 'markupsafe < 2.1'
 
 # Run the playbook again in the venv with Jinja < 2.10
 ansible-playbook runme.yml "$@"