Bump sequelize from 5.1.0 to 5.15.1 in /examples/simple

Bumps [sequelize](https://github.com/sequelize/sequelize) from 5.1.0 to 5.15.1.
- [Release notes](https://github.com/sequelize/sequelize/releases)
- [Commits](sequelize/sequelize@v5.1.0...v5.15.1)

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

Author: dependabot[bot]

examples/simple/package-lock.json

@@ -17,7 +17,7 @@
   "dependencies": {
     "body-parser": "^1.18.3",
     "express": "^4.16.4",
-    "sequelize": "^5.1.0",
+    "sequelize": "^5.15.1",
     "sequelize-typescript": "^1.0.0-alpha.9",
     "strong-error-handler": "^3.2.0"
   }