chore: bump mongodb 3.1.4 and mongodb-core 3.1.3

Fix underlying library issues
Fix Automattic#6903, Resolve Automattic#6884, Re: Automattic#6869

Author: Fonger

package.json

@@ -23,8 +23,8 @@
     "bson": "~1.0.5",
     "kareem": "2.2.1",
     "lodash.get": "4.4.2",
-    "mongodb": "3.1.3",
-    "mongodb-core": "3.1.2",
+    "mongodb": "3.1.4",
+    "mongodb-core": "3.1.3",
     "mongoose-legacy-pluralize": "1.0.2",
     "mpath": "0.4.1",
     "mquery": "3.2.0",