Bump mongoose from 5.13.14 to 5.13.15

Bumps [mongoose](https://github.com/Automattic/mongoose) from 5.13.14 to 5.13.15.
- [Release notes](https://github.com/Automattic/mongoose/releases)
- [Changelog](https://github.com/Automattic/mongoose/blob/master/CHANGELOG.md)
- [Commits](Automattic/mongoose@5.13.14...5.13.15)

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

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

Author: dependabot[bot]

package-lock.json

@@ -12,7 +12,7 @@
     "debug": "~2.6.3",
     "ejs": "~3.1.7",
     "express": "^4.17.1",
-    "mongoose": "^5.6.0",
+    "mongoose": "^5.13.15",
     "morgan": "^1.9.1",
     "nodemon": "^2.0.4",
     "serve-favicon": "~2.4.2",