AppVeyor: Force python 3

appveyor.yml

@@ -13,19 +13,20 @@ environment:
 # scripts that are called at very beginning, before repo cloning
 init:
   - "ECHO %PYTHON% %PYTHON_VERSION% %PYTHON_ARCH%"
-  - set PATH=%PYTHON%;%PYTHON%\Scripts;%PATH%
+  - "SET PATH=%PYTHON%;%PYTHON%\Scripts;%PATH%"
+  - "python -m pip install --upgrade pip wheel"
   # Git command run locally during testing with throw-away repos; values don't matter.
   - git config --global user.email "automation@kintyre.co"
   - git config --global user.name "App Veyor"
 
 install:
   - echo PATH=%PATH%
   - python --version
-  - pip --version
-  - pip install -r requirements-ci.txt
-  - pip install .
+  - python -m pip --version
+  - python -m pip install -r requirements-ci.txt
+  - python -m pip install .
   # This will report setuptools and wheel
-  - pip freeze --all
+  - python -m pip freeze --all
 
 test_script:
   - ksconf --version