Set up build matrix for python 2.7, 3.6, 3.7

Author: terriko

.github/workflows/pythonapp.yml

@@ -6,13 +6,15 @@ jobs:
   build:
 
     runs-on: ubuntu-latest
-
+    strategy:
+      matrix:
+         python: [2.7, 3.6, 3.7]
     steps:
     - uses: actions/checkout@v1
-    - name: Set up Python 3.7
+    - name: Set up Python
       uses: actions/setup-python@v1
       with:
-        python-version: 3.7
+        python-version: ${{ matrix.python }}
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip