fix(package): update supertest to version 4.0.2

Closes #7

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
     "pretty-quick": "^1.6.0",
     "sequelize": "^4.38.0",
     "superagent": "3.8.3",
-    "supertest": "3.1.0"
+    "supertest": "4.0.2"
   },
   "devDependencies": {
     "babel-cli": "6.26.0",