Add release 2.1.31 information to appcast.xml

Added details for release 2.1.31 including new features and system requirements.

Author: sbarex

appcast.xml

@@ -3,9 +3,44 @@
     <channel>
         <title>Syntax Highlight</title>
 
+        <item>
+            <title>2.1.31</title>
+            <pubDate>mar, 15 settembre 2026 16:19:00 +0100</pubDate>
+            <sparkle:minimumSystemVersion>12.0</sparkle:minimumSystemVersion>
+            <enclosure 
+                       type="application/octet-stream" 
+                       url="https://github.com/sbarex/SourceCodeSyntaxHighlight/releases/download/2.1.31/Syntax.Highlight.zip" 
+                       sparkle:shortVersionString="2.1.31" sparkle:version="80" 
+                       sparkle:edSignature="FgXKZeFlKkxnKwasw28Ogwjv/niE3cktv5o1ieqflNdRjuaTwS2jMTmz179Ziy/NVXbcJrgHGsM5mgBSHmu3Aw==" length="14895345"
+            />
+            <description><![CDATA[
+                <h2>Release 2.1.31 (80)</h2>
+                <p align="center">If you like this app, <a href="https://www.buymeacoffee.com/sbarex">buy me a coffee!</a></p>
+                <p><strong>This release require macOS 12.0 or later.</strong></p>
+                <p>New features:</p>
+                <ul>
+                    <li>Update Highlight to release 4.21.</li>
+                    <li>Update Lua to release 5.5.1.</li>
+                    <li>Support for show indent guide lines.</li>
+                    <li>Support for <code>.robot</code> <i>as <code>python</code></i>.</li>
+                    <li>Support for the GPS eXchange Format (<code>.gpx</code>) <i>as <code>XML</code></i>.</li>
+                    <li>Support for Mill files (<code>.mill</code>) <i>as <code>Scala</code></i>.</li>
+                    <li>Support for Babashka files (<code>.bb</code>) <i>as <code>Clojure</code></i>.</li>
+                    <li>Support for OpenSCAD files (<code>.scad</code>) <i>as <code>CPP</code></i>.</li>
+                    <li>Support for <code>.env</code> files <i>as <code>INI</code></i></li>
+                    <li><code>Svelte</code> supported with a native language definition.</li>
+                </ul>
+                <p>If you like this app, <a href="https://www.buymeacoffee.com/sbarex">buy me a coffee!</a></p>
+                
+                <p><a href="https://github.com/sbarex/SourceCodeSyntaxHighlight/blob/master/CHANGELOG.md">See the complete changelog.</a></p>
+            ]]>
+            </description>
+        </item>
+        
+
         <item>
             <title>2.1.30</title>
-            <pubDate>mar, 14 apri 2026 20:29:00 +0100</pubDate>
+            <pubDate>mar, 14 aprile 2026 20:29:00 +0100</pubDate>
             <sparkle:minimumSystemVersion>10.15</sparkle:minimumSystemVersion>
             <enclosure 
                        type="application/octet-stream"