ci: test on later node versions

Author: domoritz

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
       - uses: actions/checkout@v1
       - uses: actions/setup-node@v1
         with:
-          node-version: 14
+          node-version: 15
       - name: Lint
         run: |
           yarn --frozen-lockfile
@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [12, 14, 15]
+        node-version: [14, 15]
     steps:
       - uses: actions/checkout@v1
       - uses: actions/setup-node@v1