ci: add Node.js 20 in the test matrix

Author: darrachequesne

.github/workflows/ci.yml

@@ -16,7 +16,9 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [10.x, 12.x, 14.x]
+        node-version:
+          - 10
+          - 20
 
     steps:
       - name: Checkout repository