Bump node-fetch from 2.6.1 to 2.6.7 in /preview

Bumps [node-fetch](https://github.com/node-fetch/node-fetch) from 2.6.1 to 2.6.7.
- [Release notes](https://github.com/node-fetch/node-fetch/releases)
- [Commits](https://github.com/node-fetch/node-fetch/compare/v2.6.1...v2.6.7)

---
updated-dependencies:
- dependency-name: node-fetch
  dependency-type: direct:production
...

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

preview/package.json

@@ -13,6 +13,6 @@
   "dependencies": {
     "express": "^4.17.1",
     "http-proxy-middleware": "^1.1.0",
-    "node-fetch": "^2.6.1"
+    "node-fetch": "^2.6.7"
   }
 }