[chore] Bump engine.io to version 1.8.1 (#2765)

Author: darrachequesne

package.json

@@ -25,7 +25,7 @@
   },
   "dependencies": {
     "debug": "2.3.3",
-    "engine.io": "1.8.0",
+    "engine.io": "1.8.1",
     "has-binary": "0.1.7",
     "object-assign": "4.1.0",
     "socket.io-adapter": "0.5.0",