chore(package): update supertest to version 4.0.1

Closes #40

Author: greenkeeper[bot]

package.json

@@ -62,7 +62,7 @@
     "sinon": "latest",
     "sinon-chai": "latest",
     "strong-error-handler": "^2.1.0",
-    "supertest": "^3.0.0",
+    "supertest": "^4.0.1",
     "semantic-release": "^6.3.6"
   },
   "config": {