Stop testing against Node 12

.github/workflows/ci.yml

@@ -5,14 +5,11 @@ on: [push, pull_request]
 jobs:
   test:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        node: [12, 14]
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v1
         with:
-          node-version: ${{ matrix.node }}
+          node-version: 14
       - run: npm install -g npm@7
       - run: npm ci
       - run: npm test