Don't use tox in appveyor

Author: kngwyu

appveyor.yml

@@ -23,4 +23,4 @@ test_script:
   - cargo build --verbose --all
   - cargo test --verbose --all
   - rustdoc --test README.md -L native="%PYTHON%\\libs" -L target/debug/deps/
-  - cd examples/simple-extension && python -m tox
+  - cd examples/simple-extension && python setup.py --install && python setup.py test

examples/simple-extension/tox.ini

@@ -1,5 +1,6 @@
 [tox]
-envlist = py36,
+envlist = py35,
+          py36,
           py37,
 minversion = 2.9.0
 skip_missing_interpreters = true