chore(deps): update dependency @types/node to v9.6.20

Author: renovate-bot

package.json

@@ -73,7 +73,7 @@
   },
   "devDependencies": {
     "@types/mocha": "2.2.48",
-    "@types/node": "9.6.19",
+    "@types/node": "9.6.20",
     "ban-sensitive-files": "1.9.2",
     "dependency-check": "2.10.1",
     "deps-ok": "1.4.1",