docs(demo): present the editor sample in English

web/demo.html

@@ -1,9 +1,9 @@
 <!doctype html>
-<html lang="zh-CN" data-rm-fonts="loading">
+<html lang="en" data-rm-fonts="loading">
   <head>
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover" />
-    <title>RawMark 编辑器演示</title>
+    <title>RawMark Editor Demo</title>
   </head>
   <body>
     <div id="app"></div>