Update nyc to the latest version 🚀 (#55)

## The devDependency [nyc](https://github.com/istanbuljs/nyc) was updated from `12.0.2` to `13.2.0`.
This version is **not covered** by your **current version range**.

If you don’t accept this pull request, your project will work just like it did before. However, you might be missing out on a bunch of new features, fixes and/or performance improvements from the dependency update.

---

[Find out more about this release](https://github.com/istanbuljs/nyc).

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package.json

@@ -32,7 +32,7 @@
     "eslint-config-airbnb-base": "^13.1.0",
     "eslint-plugin-import": "^2.14.0",
     "mocha": "^5.0.0",
-    "nyc": "^12.0.1",
+    "nyc": "^13.2.0",
     "rollup": "^1.0.0",
     "rollup-plugin-babel": "^4.0.2"
   }