fix: package.json & package-lock.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-SEQUELIZE-174167

Author: snyk-bot

package-lock.json

@@ -81,7 +81,7 @@
     "pm2": "^3.4.0",
     "request": "^2.88.0",
     "request-promise": "^4.2.4",
-    "sequelize": "^5.1.0",
+    "sequelize": "^5.3.0",
     "supertest": "^4.0.2",
     "swig": "^1.4.2",
     "winston": "^3.2.1",