Temporarily upper-bounce acceptance toxenv urllib3 (#318)

We're being slightly bad here and using an unpinned set of dependencies,
which has finally come back to bite us.

We can probably can oribably generate some requirements files to
fully pin things OR we can use a single venv for all this
(i.e., use the normal env with our dev dependencies) - but these will
all take a little longer than I/we want to dedicate to this right now
so the fastest "fix" is to simply add an upper-bound to urllib3 so that
pip's resolver no longer complains about version conflicts

Author: nemacysts

tox.ini

@@ -77,6 +77,7 @@ deps =
     docker-compose
     boto3
     simplejson
+    urllib3<1.27
 commands =
     docker-compose -f acceptance/docker-compose.yaml down
     docker-compose -f acceptance/docker-compose.yaml pull