Enable travis on Windows

.travis.yml

@@ -3,12 +3,21 @@ python:
 - 3.5
 - 3.6
 dist: trusty
+matrix:
+  include:
+    - os: windows
+      language: sh
+      python: "3.7"
+      before_install:
+        - choco install python3 make
+        - export PATH="/c/Python37:/c/Python37/Scripts:$PATH"
+        - python -m pip install --upgrade pip wheel
 install:
-- pip install -r requirements-dev.txt
-- pip install -e .
-- pip freeze
+  - pip install -r requirements-dev.txt
+  - pip install -e .
+  - pip freeze
 script:
-- set -eo pipefail
-- make test
+  - set -eo pipefail
+  - make test
 after_success:
-- bash <(curl -s https://codecov.io/bash)
+  - bash <(curl -s https://codecov.io/bash)