chore: codecov to dev deps (#199)

Author: alexander-fenster

handwritten/firestore/.circleci/config.yml

@@ -94,9 +94,6 @@ jobs:
             if ! test -x "$repo_tools"; then
               chmod +x "$repo_tools"
             fi
-      - run:
-          name: Install codecov.
-          command: npm install codecov
       - run:
           name: Run unit tests.
           command: npm test