chore(deps): pin dependency @types/gulp to 4.0.6

Author: renovate-bot

package.json

@@ -84,7 +84,7 @@
     "@types/cors": "2.8.5",
     "@types/express": "4.17.0",
     "@types/fastify-cors": "2.1.0",
-    "@types/gulp": "^4.0.6",
+    "@types/gulp": "4.0.6",
     "@types/kafka-node": "2.0.8",
     "@types/mocha": "5.2.7",
     "@types/node": "10.14.13",