fix(package): update supertest to version 4.0.0

Author: greenkeeper[bot]

package.json

@@ -71,7 +71,7 @@
     "request": "^2.88.0",
     "request-promise": "^4.2.4",
     "sequelize": "^4.43.0",
-    "supertest": "^3.4.2",
+    "supertest": "^4.0.0",
     "swig": "^1.4.2",
     "winston": "^3.2.1",
     "zxcvbn": "^4.4.2",