chore(package): update mongodb to version 2.2.7 (#2554)

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -29,7 +29,7 @@
     "lru-cache": "4.0.1",
     "mailgun-js": "0.7.10",
     "mime": "1.3.4",
-    "mongodb": "2.2.5",
+    "mongodb": "2.2.7",
     "multer": "1.2.0",
     "parse": "1.9.1",
     "parse-server-fs-adapter": "1.0.1",