Tests: Require tox < 3.1 to avoid basepython conflicts

diff --git a/appveyor.yml b/appveyor.yml
index 41b1cb21b318acf539c7e2f3ffd0c6f8950db612..fbe893a4d9b533ab92c0778f9ccd76449270465e 100644 (file)
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -51,7 +51,7 @@ install:
   - "python --version"
   - "python -c \"import struct; print(struct.calcsize('P') * 8)\""
   - "python -m pip install --upgrade pip setuptools"
-  - "pip install --upgrade tox ppu"
+  - "pip install --upgrade \"tox < 3.1\" ppu"
   - "pip --version"
 
 # No build step