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

@@ -36,7 +36,7 @@
     "react": "15.4.0",
     "react-adsense": "0.0.5",
     "react-dom": "15.4.0",
-    "sequelize": "3.27.0",
+    "sequelize": "5.15.1",
     "source-map-support": "0.4.6",
     "sqlite3": "3.1.8",
     "universal-analytics": "^0.4.8",