Update away from vulnerable version of node-fetch (#135)

Backporting #124 to the 2.x branch for dependencies stuck on that which can't get a PR for moving on reviewed, e.g. MetaMask/web3-provider-engine#404

package.json

@@ -61,7 +61,7 @@
     "url": "https://github.com/lquixada/cross-fetch/issues"
   },
   "dependencies": {
-    "node-fetch": "^2.6.1",
+    "node-fetch": "^2.6.7",
     "whatwg-fetch": "2.0.4"
   },
   "devDependencies": {