ci: only upload coverage to codecov once

Author: ryanio

.github/workflows/build.yml

@@ -21,9 +21,9 @@ jobs:
       - uses: actions/checkout@v2
       - run: npm install
       - run: npm run lint
-      - run: npm run build
       - run: npm run coverage
       - uses: codecov/codecov-action@v1
+        if: matrix.node-version == 12
         with:
           file: ./coverage/lcov.info
   test-browser: