chore(package): update supertest to version 4.0.2

Closes #29

Author: greenkeeper[bot]

package.json

@@ -32,7 +32,7 @@
     "express": "^4.16.3",
     "mocha": "^5.2.0",
     "should": "^13.2.3",
-    "supertest": "^3.1.0"
+    "supertest": "^4.0.2"
   },
   "dependencies": {}
 }