Fixed yaml syntax

Author: seanlaw

.github/workflows/github-actions.yml

@@ -1,3 +1,17 @@
 name: github-actions
 on: [push, pull_request]
-jobs
+jobs:
+  unit-testing:
+    runs-on: {{ matrix.os }}
+      strategy:
+        matrix:
+          os: [ubuntu-latest, macos-latest, windows-latest]
+          python-version: [3.6', '3.7', '3.8']
+      steps:
+        - uses: actions/checkout@v2
+        - name: Set up Python
+          uses: actions/setup-python@v2
+          with:
+            python-version: ${{ matrix.python-version }}
+        - name: Display Python version
+          run: python -c "import sys; print(sys.version)"