Bump sequelize from 4.41.0 to 5.15.1

Bumps [sequelize](https://github.com/sequelize/sequelize) from 4.41.0 to 5.15.1.
- [Release notes](https://github.com/sequelize/sequelize/releases)
- [Commits](sequelize/sequelize@v4.41.0...v5.15.1)

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

Author: dependabot[bot]

package-lock.json

@@ -20,7 +20,7 @@
     "nodemon": "^1.18.9",
     "pg": "^7.6.0",
     "pg-hstore": "^2.3.2",
-    "sequelize": "^4.41.0",
+    "sequelize": "^5.15.1",
     "sequelize-cli": "^5.3.0",
     "serve-favicon": "^2.5.0"
   },