Update windows tests to test both versions

This fixes #44 by testing the automatic import, the legacy version, and
the modern version directtly.

.travis.yml

@@ -9,6 +9,7 @@ matrix:
         - choco install python3 --params "/InstallDir:C:\Python"
         - export PATH="/c/Python:/c/Python/Scripts:$PATH"
         - python -m pip install --upgrade pip
+        - python -m pip install pywin32
       before_script:
         - export TOXENV=py3-win