fix: make fetch behave when testing.

When testing the nock package does not know how to behave with the native fetch, so we use 'node-fetch' to make fetch testable with nock. More info: nock/nock#2397 (comment)

package.json

@@ -42,7 +42,7 @@
   "main": "index.js",
   "scripts": {
     "release": "release-it",
-    "test": "mocha \"test/**/*.js\" --reporter spec",
+    "test": "mocha \"test/**/*.js\" --reporter spec --no-experiemental-fetch",
     "prepare": "husky install",
     "lint": "eslint src/ test/"
   }