Limit node-version to 12.x in CI (#7)

Author: trivikr

.github/workflows/build.yml

@@ -9,7 +9,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [12.x, 14.x, 16.x]
+        node-version: [12.x]
 
     steps:
       - uses: actions/checkout@v2