update node-version matrix; add v18 and remove v12

Author: eitoball

.github/workflows/main.yml

@@ -12,7 +12,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: ['12', '14', '16']
+        node-version: ['14', '16', '18']
 
     steps:
       - uses: actions/checkout@v3