chore(deps): update dependency supertest to v6

Author: renovate-bot

package-lock.json

@@ -43,7 +43,7 @@
     "jest": "24.9.0",
     "rimraf": "3.0.0",
     "source-map-support": "0.5.13",
-    "supertest": "4.0.2",
+    "supertest": "6.2.3",
     "ts-jest": "24.1.0",
     "tslint": "5.20.0",
     "tslint-config-prettier": "1.18.0",