Updates node versions testing against

Drop node 12.x we are currently (and have been for 
some time now) developing on 14.18 and 16 versions.

Author: gnikit

.github/workflows/main.yaml

@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [12.x]
+        node-version: [14.x, 16.x]
     steps:
       - uses: actions/checkout@v2
       - name: Use Node.js ${{ matrix.node-version }}