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: >-