Update dependency supertest to v6

Author: renovate[bot]

package.json

@@ -36,15 +36,15 @@
   "devDependencies": {
     "@types/koa": "^2.11.3",
     "@types/node": "^14.10.3",
-    "@types/supertest": "^2.0.10",
+    "@types/supertest": "^6.0.0",
     "@types/uuid": "^8.3.0",
     "@typescript-eslint/eslint-plugin": "^4.12.0",
     "@typescript-eslint/parser": "^4.12.0",
     "eslint": "^7.9.0",
     "jest": "^26.6.3",
     "gts": "^2.0.2",
     "koa": "^2.13.0",
-    "supertest": "^4.0.2",
+    "supertest": "^6.0.0",
     "ts-jest": "^26.4.2",
     "ts-node": "^9.0.0",
     "typescript": "^4.0.3"