fix(package): update mongodb to version 2.2.31 (#4089)

Author: greenkeeper[bot]

package.json

@@ -27,7 +27,7 @@
     "lodash": "4.17.4",
     "lru-cache": "4.1.1",
     "mime": "1.3.6",
-    "mongodb": "2.2.30",
+    "mongodb": "2.2.31",
     "multer": "1.3.0",
     "parse": "1.10.0",
     "parse-server-fs-adapter": "1.0.1",