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

@@ -45,7 +45,7 @@
     "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",
     "sqlite3": "4.2.0",
     "universal-analytics": "0.4.20",