Travis CI: Add parallel test runs on macOS and Windows

.travis.yml

@@ -1,21 +1,38 @@
 dist: xenial
 language: python
 cache: pip
-python:
-    - 2.7
-    - 3.7
+matrix:
+  include:
+    - name: "Python 2.7 on Linux"
+      python: 2.7
+    - name: "Python 3.7 on Linux"
+      python: 3.7
+    - name: "Python 2.7 on macOS"
+      os: osx
+      osx_image: xcode10.2
+      language: shell  # 'language: python' is not yet supported on macOS
+      before_install: HOMEBREW_NO_AUTO_UPDATE=1 brew install npm
+    - name: "Python 2.7 on Windows"
+      os: windows
+      language: node_js
+      node_js: 12  # node
+      env: PATH=/c/Python27:/c/Python27/Scripts:$PATH
+      before_install: choco install python2
+  allow_failures:
+    - os: windows
 install:
-    #- pip install -r requirements.txt
-    - pip install flake8  # pytest  # add another testing frameworks later
+  #- pip install -r requirements.txt
+  - pip install flake8  # pytest  # add another testing frameworks later
 before_script:
-    # stop the build if there are Python syntax errors or undefined names
-    - flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics
-    # exit-zero treats all errors as warnings.  The GitHub editor is 127 chars wide
-    - flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
-    - npm install
+  - flake8 --version
+  # stop the build if there are Python syntax errors or undefined names
+  - flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics
+  # exit-zero treats all errors as warnings.  Two space indentation is OK.  The GitHub editor is 127 chars wide
+  - flake8 . --count --exit-zero --ignore=E111,E114,W503 --max-complexity=10 --max-line-length=127 --statistics
+  - npm install
 script:
-    - npm test
-    #- pytest --capture=sys  # add other tests here
+  - npm test
+  #- pytest --capture=sys  # add other tests here
 notifications:
-    on_success: change
-    on_failure: change  # `always` will be the setting once code changes slow down
+  on_success: change
+  on_failure: change  # `always` will be the setting once code changes slow down