discontinue testing on Node.js 12 (end-of-life)

Author: jstritch

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
       matrix:
         # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
         # See supported os at https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners
-        node-version: [12, 14, 16]
+        node-version: [14, 16]
         os: [ubuntu-latest, macos-latest, windows-latest]
 
     runs-on: ${{ matrix.os }}