fix: process.cwd error

在调用build/util/loadEnv()函数时会报process.cwd() is not a function

#44

index.html

@@ -7,8 +7,9 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>后台管理系统</title>
     <script src="/sortable.min.js"></script>
-    <script>
-      window.process = {};
+    <script type="module">
+      import process from "process";
+      window.process = process;
     </script>
   </head>