Update mongodb requirement from 3.1.8 to 3.2.7

Updates the requirements on [mongodb](https://github.com/mongodb/node-mongodb-native) to permit the latest version.
- [Release notes](https://github.com/mongodb/node-mongodb-native/releases)
- [Changelog](https://github.com/mongodb/node-mongodb-native/blob/master/HISTORY.md)
- [Commits](mongodb/node-mongodb-native@v3.1.8...v3.2.7)

package.json

@@ -18,7 +18,7 @@
     "@slack/web-api": "^5.0.1",
     "bcrypt-nodejs": "0.0.3",
     "formidable": "^1.2.1",
-    "mongodb": "3.1.8",
+    "mongodb": "3.2.7",
     "node-cache": "4.2.0",
     "node-schedule": "1.3.2",
     "snyk": "^1.161.1"