Create .travis.yml

.travis.yml

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+language: python            # this works for Linux but is an error on macOS or Windows
+jobs:
+  include:
+    - name: "Python 3.8.0 on Xenial Linux"
+      python: 3.8           # this works for Linux but is ignored on macOS or Windows
+    - 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 3.7.4 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: 
+  - pip3 install --upgrade pip  # all three OSes agree about 'pip3'
+# 'python' points to Python 2.7 on macOS but points to Python 3.8 on Linux and Windows
+# 'python3' is a 'command not found' error on Windows but 'py' works on Windows only
+  - pip3 install -r requirements.txt
+script: python3 __main__.py || python __main__.py