Update deno.json

Author: knotbin

deno.json

@@ -3,7 +3,7 @@
     "ok": "deno fmt --check && deno lint && deno check",
     "dev": "deno run -A --env --watch=static/,routes/ dev.ts",
     "build": "deno run -A dev.ts build",
-    "start": "deno run -A main.ts",
+    "preview": "deno serve -A _fresh/server.js",
     "update": "deno run -A -r jsr:@fresh/update ."
   },
   "lint": {