test_wheel: Fix for Python 3.4

[skip ci]

makepanda/test_wheel.py

@@ -50,8 +50,12 @@ def test_wheel(wheel, verbose=False):
 
     # Install pytest into the environment, as well as our wheel.
     packages = ["pytest", wheel]
-    if sys.version_info[0:2] == (3, 4) and sys.platform == "win32":
-        packages += ["colorama==0.4.1"]
+    if sys.version_info[0:2] == (3, 4):
+        if sys.platform == "win32":
+            packages += ["colorama==0.4.1"]
+
+        # See https://github.com/python-attrs/attrs/pull/807
+        packages += ["attrs<21"]
 
     if subprocess.call([python, "-m", "pip", "install"] + packages) != 0:
         shutil.rmtree(envdir)