fix(package): update sequelize to version 5.21.5

Closes #33

Author: greenkeeper[bot]

package.json

@@ -18,7 +18,7 @@
     "minio": "^7.0.3",
     "pg": "^7.4.3",
     "pg-hstore": "^2.3.2",
-    "sequelize": "^4.22.6",
+    "sequelize": "^5.21.5",
     "uuid": "^3.3.2"
   },
   "devDependencies": {