ci: add Node.js v16 to test matrix

Author: antongolub

.github/workflows/CI.yml

@@ -8,7 +8,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [10.x, 12.x, 14.x]
+        node-version: [10.x, 12.x, 14.x, 16.x]
 
     steps:
       - uses: actions/checkout@v2