Update dependency parse-server to v2.8.4

Author: renovate[bot]

appengine/parse-server/package.json

@@ -10,7 +10,7 @@
   },
   "dependencies": {
     "express": "4.16.4",
-    "parse-server": "2.7.2",
+    "parse-server": "2.8.4",
     "nconf": "0.10.0"
   }
 }