Bump node-fetch from 2.2.1 to 2.6.1 in /sdk

Bumps [node-fetch](https://github.com/bitinn/node-fetch) from 2.2.1 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@v2.2.1...v2.6.1)

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

sdk/package.json

@@ -21,7 +21,7 @@
   "dependencies": {
     "dom-storage": "2.1.0",
     "is-plain-object": "2.0.4",
-    "node-fetch": "2.2.1"
+    "node-fetch": "2.6.1"
   },
   "devDependencies": {
     "@ringcentral/sdk-utils": "*",