Test old Node.js versions.

- Align with current travis config.
- Support for older verions will be dropped over time.

Author: davidlehn

.github/workflows/main.yml

@@ -8,7 +8,7 @@ jobs:
     timeout-minutes: 10
     strategy:
       matrix:
-        node-version: [10.x, 12.x, 14.x]
+        node-version: [6.x, 8.x, 10.x, 12.x, 14.x]
     steps:
     - uses: actions/checkout@v2
     - name: Use Node.js ${{ matrix.node-version }}