Tests: Require tox < 3.1 to avoid basepython conflicts

diff --git a/appveyor.yml b/appveyor.yml
index 5c50ceeb14e10e7b178a4973f702f5836abf1c43..16dda7d5eaf637f8c326f3940081a94a782a40cb 100644 (file)
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -54,7 +54,7 @@ install:
   - "python --version"
   - "python -c \"import struct; print(struct.calcsize('P') * 8)\""
   - "python -m pip install --upgrade pip setuptools"
-  - "pip install --upgrade tox"
+  - "pip install --upgrade \"tox < 3.1\" ppu"
   - "pip --version"
 
 # No build step - we don't have C extensions