chore(package): update supertest to version 3.4.1

Closes #27

Author: greenkeeper[bot]

package.json

@@ -47,6 +47,6 @@
     "mocha": "^3.3.0",
     "sinon": "^2.1.0",
     "sinon-chai": "^2.9.0",
-    "supertest": "^2.0.1"
+    "supertest": "^3.4.1"
   }
 }