Update dependency parse-server to v3 (#967)

Author: renovate[bot]

appengine/parse-server/package.json

@@ -10,7 +10,7 @@
   },
   "dependencies": {
     "express": "4.16.4",
-    "parse-server": "2.8.4",
+    "parse-server": "3.1.2",
     "nconf": "0.10.0"
   }
 }