fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-DOTTIE-3332763

package.json

@@ -66,7 +66,7 @@
     "normalize-registry-metadata": "^1.1.2",
     "rimraf": "^2.6.2",
     "semver": "^5.4.1",
-    "sequelize": "^3.23.4",
+    "sequelize": "^4.0.0",
     "ssri": "^8.0.1",
     "thunkify-wrap": "^1.0.4",
     "treekill": "^1.0.0",