[pkg] Update ioredis to version 4.16.0 (#69)

package.json

@@ -32,7 +32,7 @@
   },
   "devDependencies": {
     "assume": "~2.2.0",
-    "ioredis": "~4.14.0",
+    "ioredis": "~4.16.0",
     "mocha": "~6.2.0",
     "pre-commit": "~1.2.0"
   }