Update healthcheck.js

fix healthcheck output error: "file:///usr/src/app/src/healthcheck.js:1\nvar http = require(\"http\");\n           ^\n\nReferenceError: require is not defined in ES module scope, you can use import instead\nThis file is being treated as an ES module because it has a '.js' file extension and '/usr/src/app/package.json' contains \"type\": \"module\". To treat it as a CommonJS script, rename it to use the '.cjs' file extension.\n    at file:///usr/src/app/src/healthcheck.js:1:12\n    at ModuleJob.run (node:internal/modules/esm/module_job:193:25)\n    at async Promise.all (index 0)\n    at async ESMLoader.import (node:internal/modules/esm/loader:526:24)\n    at async loadESM (node:internal/process/esm_loader:91:5)\n    at async handleMainPromise (node:internal/modules/run_main:65:12)\n"

src/healthcheck.js

@@ -1,4 +1,4 @@
-var http = require("http");
+import * as http from 'http';
 var options = {
   timeout: 2000,
 };