Bump sequelize from 3.27.0 to 5.15.1

Bumps [sequelize](https://github.com/sequelize/sequelize) from 3.27.0 to 5.15.1.
- [Release notes](https://github.com/sequelize/sequelize/releases)
- [Commits](sequelize/sequelize@v3.27.0...v5.15.1)

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

Author: dependabot[bot]

package.json

@@ -47,7 +47,7 @@
     "react-hot-loader": "^3.1.3",
     "redbox-react": "^1.6.0",
     "rimraf": "^2.6.3",
-    "sequelize": "3.27.0",
+    "sequelize": "5.15.1",
     "sinon": "^2.4.1",
     "universal-analytics": "^0.4.20",
     "universal-router": "2.0.0",