jenkins: don't use pip 8

jenkins.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 
 pip install --upgrade setuptools
-pip install --upgrade pip
+pip install --upgrade 'pip<8'
 pip install --editable .
 pip install --upgrade pytest pytest-cov pytest-django pytest-mock
 pip install --upgrade WebTest==2.0.16