fix command

appveyor.yml

@@ -86,7 +86,7 @@ install:
   # compiled extensions and are not provided as pre-built wheel packages,
   # pip will build them from source using the MSVC compiler matching the
   # target Python version and architecture
-  - "%CMD_IN_ENV% pip install --upgrade pip"
+  - "%PYTHON%\\python.exe -m pip install --upgrade pip"
   - "%CMD_IN_ENV% pip install -r dev-requirements.txt"
   - "%CMD_IN_ENV% python -c \"import os,subprocess; os.environ.get('UIA_SUPPORT')=='YES' and subprocess.check_output(['pip','install','comtypes'])\""