Added windows & macOS

.travis.yml

@@ -2,11 +2,20 @@ language: python
 
 python:
   - 3.6
-  - 3.7
   - 3.8
   - nightly
   - pypy3
-
+  - name: "Python 3.7.4 on macOS"
+    os: osx
+    osx_image: xcode11.2  # Python 3.7.4 running on macOS 10.14.4
+    language: shell       # 'language: python' is an error on Travis CI macOS
+  - name: "Python 3.8.0 on Windows"
+    os: windows           # Windows 10.0.17134 N/A Build 17134
+    language: shell       # 'language: python' is an error on Travis CI Windows
+    before_install:
+      - choco install python --version 3.8.0
+      - python -m pip install --upgrade pip
+    env: PATH=/c/Python38:/c/Python38/Scripts:$PATH
 install: 
   - pip install .
   - pip install nose coverage