fix(package): update sequelize to version 5.2.6

Closes #55

Author: greenkeeper[bot]

package.json

@@ -54,7 +54,7 @@
     "pem": "^1.13.0",
     "pg": "^7.4.1",
     "pg-hstore": "^2.3.2",
-    "sequelize": "^4.38.0",
+    "sequelize": "^5.2.6",
     "sequelize-cli": "^5.0.0",
     "ws": "latest"
   },