chore(package): update supertest to version 4.0.2

Closes #6

Author: greenkeeper[bot]

package.json

@@ -70,7 +70,7 @@
     "jsdoc": "^3.5.5",
     "semantic-release": "^15.12.4",
     "standard": "^12.0.1",
-    "supertest": "^3.3.0",
+    "supertest": "^4.0.2",
     "travis-deploy-once": "^5.0.9"
   }
 }