build: add testing on windows in Travis

.travis.yml

@@ -6,8 +6,26 @@ python:
   - 3.7
   - 3.8-dev
 
+matrix:
+  include:
+    - os: windows           # Windows 10
+      language: shell       # 'language: python' is an error on Travis CI Windows
+      python: 2.7
+      before_install:
+        - choco install python2
+        - python -m pip install --upgrade pip
+      env: PATH=/c/Python27:/c/Python27/Scripts:$PATH
+
+    - os: windows           # Windows 10
+      language: shell       # 'language: python' is an error on Travis CI Windows
+      python: 3.7
+      before_install:
+        - choco install python3
+        - python -m pip install --upgrade pip
+      env: PATH=/c/Python37:/c/Python37/Scripts:$PATH
+
 install:
-  - pip install colorama flake8
+  - python -m pip install colorama flake8
   - if [[ $(python -c "import sys; print(sys.version_info >= (3,5,))") == "True" ]]; then pip install flake8-bugbear; fi
 
 script: