Run CI with Pillow too

Author: Hugo Osvaldo Barrera

.github/workflows/tests.yml

@@ -9,7 +9,8 @@ jobs:
       matrix:
         os: [ubuntu-18.04, macOS-10.14]
         python: [ '3.5', '3.6', '3.7' ]
-    name: python${{ matrix.python }} on ${{ matrix.os }}
+        extras: [ "", "[images]" ]
+    name: python${{ matrix.python }} on ${{ matrix.os }} ${{ matrix.extras }}
     steps:
       - uses: actions/checkout@master
       - uses: actions/setup-python@v1
@@ -20,6 +21,7 @@ jobs:
         run: |
           pip install --upgrade --no-cache-dir pipenv
           pipenv install --dev
+          pipenv install .${{ matrix.extras }}
       - name: Run tests
         run: pipenv run pytest
       - name: Report coverage