build: add test run Python 3.7 on macOS

Refs: #1846
PR-URL: #1843
Reviewed-By: João Reis <reis@janeasystems.com>

.travis.yml

@@ -8,7 +8,7 @@ matrix:
  python: 2.7
  - name: "Python 2.7 on macOS"
  os: osx
- osx_image: xcode10.2
+ osx_image: xcode11
  language: shell # 'language: python' is not yet supported on macOS
  env: NODE_GYP_FORCE_PYTHON=python2
  before_install: HOMEBREW_NO_AUTO_UPDATE=1 brew install npm
@@ -28,6 +28,7 @@ matrix:
  PATH=/c/Python27:/c/Python27/Scripts:$PATH
  NODE_GYP_FORCE_PYTHON=/c/Python27/python.exe
  before_install: choco install python2
+
  - name: "Node.js 6 & Python 3.7 on Linux"
  python: 3.7
  env: NODE_GYP_FORCE_PYTHON=python3 EXPERIMENTAL_NODE_GYP_PYTHON3=1
@@ -44,6 +45,12 @@ matrix:
  python: 3.7
  env: NODE_GYP_FORCE_PYTHON=python3 EXPERIMENTAL_NODE_GYP_PYTHON3=1
  before_install: nvm install 12
+ - name: "Python 3.7 on macOS"
+ os: osx
+ #osx_image: xcode11
+ language: shell # 'language: python' is not yet supported on macOS
+ env: NODE_GYP_FORCE_PYTHON=python3 EXPERIMENTAL_NODE_GYP_PYTHON3=1
+ before_install: HOMEBREW_NO_AUTO_UPDATE=1 brew install npm
  - name: "Node.js 12 & Python 3.7 on Windows"
  os: windows
  language: node_js
@@ -53,6 +60,7 @@ matrix:
  NODE_GYP_FORCE_PYTHON=/c/Python37/python.exe
  EXPERIMENTAL_NODE_GYP_PYTHON3=1
  before_install: choco install python
+
  allow_failures:
  - env: NODE_GYP_FORCE_PYTHON=python3 EXPERIMENTAL_NODE_GYP_PYTHON3=1
  - env: >-