fix HTML errors in 2014/sinon/spoiler.html

2014/sinon/spoiler.html

@@ -1,8 +1,9 @@
 <!DOCTYPE html>
-<html><head>
+<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+<head>
+<meta charset="utf-8">
 <title>Replay text</title>
-<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
-<style type="text/css">
+<style>
 .tmp{color:#00f}.final{color:#000}</style>
 </head><body>
 <noscript><span style="color:red">JavaScript required</span></noscript>