Set up build matrix for python 3.6, 3.7

Author: terriko

.github/workflows/pythonapp.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-         python: [2.7, 3.6, 3.7]
+         python: [3.6, 3.7]
     steps:
     - uses: actions/checkout@v1
     - name: Set up Python