chore(package): update supertest to version 4.0.1

Closes #304

Author: greenkeeper[bot]

package.json

@@ -65,7 +65,7 @@
     "rsvp": "4.7.0",
     "semantic-release": "^12.2.2",
     "standard": "^10.0.3",
-    "supertest": "^3.0.0",
+    "supertest": "^4.0.1",
     "travis-deploy-once": "^4.3.1"
   },
   "standard": {