Bump mongoose from 5.7.5 to 5.13.15

Bumps [mongoose](https://github.com/Automattic/mongoose) from 5.7.5 to 5.13.15.
- [Release notes](https://github.com/Automattic/mongoose/releases)
- [Changelog](https://github.com/Automattic/mongoose/blob/master/CHANGELOG.md)
- [Commits](https://github.com/Automattic/mongoose/compare/5.7.5...5.13.15)

---
updated-dependencies:
- dependency-name: mongoose
  dependency-type: direct:production
...

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

package.json

@@ -28,7 +28,7 @@
     "connect": "^3.6.5",
     "express": "^4.16.2",
     "mongodb": "^3.1.13",
-    "mongoose": "^5.7.5",
+    "mongoose": "^5.13.15",
     "passport": "^0.4.0",
     "passport-local": "^1.0.0",
     "validator": "^13.7.0"