Update supertest requirement from ^1.2.0 to ^4.0.0

Updates the requirements on [supertest](https://github.com/visionmedia/supertest) to permit the latest version.
- [Release notes](https://github.com/visionmedia/supertest/releases)
- [Commits](ladjs/supertest@v1.2.0...v4.0.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

package.json

@@ -43,7 +43,7 @@
     "istanbul": "^0.4.1",
     "mocha": "^6.0.2",
     "sinon": "^7.0.0",
-    "supertest": "^1.2.0",
+    "supertest": "^4.0.0",
     "supertest-promised": "^1.0.0",
     "uuid": "^3.3.2"
   },