security: patch mermaid package version

https://github.com/gogs/gogs/security/advisories/GHSA-26gq-grmh-6xm6

Co-authored-by: Jakub Domeracki <jdomeracki.itsec@gmail.com>
Co-authored-by: ᴊᴏᴇ ᴄʜᴇɴ <jc@unknwon.io>

templates/base/footer.tmpl

@@ -59,7 +59,7 @@
 	<script src="{{AppSubURL}}/plugins/autosize-4.0.2/autosize.min.js"></script>
 {{end}}
 {{if .IsMarkdown}}
-	<script src="{{AppSubURL}}/plugins/mermaid-8.14.0/mermaid.min.js"></script>
+	<script src="{{AppSubURL}}/plugins/mermaid-11.12.1/mermaid.min.js"></script>
 	<script>
 		$(document).ready(function () {
 			mermaid.init({startOnLoad: true, noteMargin: 10}, ".language-mermaid");