Upgrade explorer build output

Since the next:export command is deprecated in favor of 'output: export' in next.config.js.

Author: Alenar

mithril-explorer/next.config.js

@@ -1,5 +1,6 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
+  output: "export",
   basePath: "/explorer",
   reactStrictMode: true,
   swcMinify: true,

mithril-explorer/package.json

@@ -4,7 +4,7 @@
   "private": true,
   "scripts": {
     "dev": "next dev",
-    "build": "next build && next export",
+    "build": "next build",
     "start": "next start",
     "lint": "next lint",
     "test": "jest --watch",