Bump mongodb from 2.2.33 to 3.1.13

Bumps [mongodb](https://github.com/mongodb/node-mongodb-native) from 2.2.33 to 3.1.13.
- [Release notes](https://github.com/mongodb/node-mongodb-native/releases)
- [Changelog](https://github.com/mongodb/node-mongodb-native/blob/master/CHANGES_3.0.0.md)
- [Commits](https://github.com/mongodb/node-mongodb-native/compare/v2.2.33...v3.1.13)

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -27,7 +27,7 @@
     "body-parser": "^1.18.2",
     "connect": "^3.6.5",
     "express": "^4.16.2",
-    "mongodb": "^2.2.33",
+    "mongodb": "^3.1.13",
     "mongoose": "^5.7.5",
     "passport": "^0.4.0",
     "passport-local": "^1.0.0",