This breaks under pip==20.0.2, so don't use it for now

Author: nedbat

requirements/tox.pip

@@ -4,4 +4,5 @@
 # The version of tox used by coverage.py
 tox==3.14.3
 # Adds env recreation on requirements file changes.
-tox-battery==0.5.1
+# Waiting for https://github.com/signalpillar/tox-battery/issues/19
+#tox-battery==0.5.1