Bump mongodb from 2.2.36 to 3.1.13

Bumps [mongodb](https://github.com/mongodb/node-mongodb-native) from 2.2.36 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](mongodb/node-mongodb-native@v2.2.36...v3.1.13)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package-lock.json

@@ -15,7 +15,7 @@
     "forever": "^2.0.0",
     "helmet": "^2.0.0",
     "marked": "0.3.9",
-    "mongodb": "^2.1.18",
+    "mongodb": "^3.1.13",
     "needle": "2.2.4",
     "node-esapi": "0.0.1",
     "serve-favicon": "^2.3.0",