Bump node-fetch from 1.7.1 to 2.6.1

Bumps [node-fetch](https://github.com/bitinn/node-fetch) from 1.7.1 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@v1.7.1...v2.6.1)

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

package.json

@@ -62,7 +62,7 @@
     "eslint-plugin-import": "^2.6.1",
     "husky": "^0.14.1",
     "mocha": "^3.4.2",
-    "node-fetch": "^1.7.1",
+    "node-fetch": "^2.6.1",
     "nyc": "^11.0.3",
     "rimraf": "^2.6.1",
     "sinon": "^2.3.6",