Update dependency supertest to v7

Author: renovate[bot]

package.json

@@ -15,6 +15,6 @@
     "chai": "4.2.0",
     "koa": "2.5.3",
     "mocha": "2.5.3",
-    "supertest": "3.2.0"
+    "supertest": "7.0.0"
   }
 }