add osx

.travis.yml

@@ -24,6 +24,10 @@ matrix:
          - TOXENV=py37
          - PATH=/c/Python37:/c/Python37/Scripts:$PATH
          - ESCPOS_CAPABILITIES_FILE=C:/Users/travis/build/python-escpos/python-escpos/capabilities-data/dist/capabilities.json
+    - name: "Python 3.7 on macOS"
+      os: osx
+      osx_image: xcode10.2
+      language: shell
     - python: 2.7
       env: TOXENV=py27
     - python: 3.4
@@ -57,7 +61,7 @@ matrix:
     - python: 3.8-dev
     - python: nightly
     - python: pypy3
-    - os: windows
+    - os: windows osx
 before_install:
     - pip install tox codecov 'sphinx>=1.5.1'
     - ./doc/generate_authors.sh --check