fix HTML errors in 2018/yang/spoiler.html

2018/yang/spoiler.html

@@ -2,6 +2,7 @@
 <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
 <head>
 <meta charset="utf-8">
+<title>Replay text</title>
 <style>
 .tmp{color:#00f}.final{color:#000}</style>
 </head><body>