Bump codecov from 2.3.1 to 3.8.3

Bumps [codecov](https://github.com/codecov/codecov-node) from 2.3.1 to 3.8.3.
- [Release notes](https://github.com/codecov/codecov-node/releases)
- [Changelog](https://github.com/codecov/codecov-node/blob/master/CHANGELOG.md)
- [Commits](codecov/codecov-node@v2.3.1...v3.8.3)

---
updated-dependencies:
- dependency-name: codecov
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package-lock.json

@@ -91,7 +91,7 @@
     "babel-register": "^6.4.3",
     "chai": "^3.5.0",
     "chai-spies": "^0.7.1",
-    "codecov": "^2.1.0",
+    "codecov": "^3.7.1",
     "cross-env": "^5.2.1",
     "css-loader": "^0.22.0",
     "documentation": "4.0.0-rc.1",