Bump node-fetch from 1.7.3 to 2.6.1

Bumps [node-fetch](https://github.com/bitinn/node-fetch) from 1.7.3 to 2.6.1.
- [Release notes](https://github.com/bitinn/node-fetch/releases)
- [Changelog](https://github.com/node-fetch/node-fetch/blob/master/docs/CHANGELOG.md)
- [Commits](node-fetch/node-fetch@1.7.3...v2.6.1)

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

Author: dependabot[bot]

package-lock.json

@@ -30,6 +30,6 @@
   "devDependencies": {
     "jsdoc": "^3.5.3",
     "mocha": "^6.1.4",
-    "node-fetch": "^1.6.3"
+    "node-fetch": "^2.6.1"
   }
 }