fix: make copy button copy raw markdown

layouts/_default/single.html

@@ -1,7 +1,7 @@
 {{ define "title" }}{{ .Title }} | {{ .Site.Title }}{{ end }}
 
 {{ define "main" }}
-    <div class="coc-box">
+    <div class="coc-box" data-raw-content="{{ .RawContent }}">
         <button class="copy-btn" onclick="copyCoC()">[copy]</button>
         {{ .Content }}
     </div>