Update appcast.xml

Author: intitni

appcast.xml

@@ -10,9 +10,9 @@
       <sparkle:shortVersionString>0.15.4</sparkle:shortVersionString>
       <sparkle:minimumSystemVersion>12.0</sparkle:minimumSystemVersion>
       <sparkle:releaseNotesLink>
-        https://github.com/intitni/CopilotForXcode/releases/tag/0.15.4
+        https://github.com/intitni/CopilotForXcode/releases/tag/0.15.3
       </sparkle:releaseNotesLink>
-      <enclosure url="https://github.com/intitni/CopilotForXcode/releases/download/0.15.4/Copilot.for.Xcode.app.zip" length="21344856" type="application/octet-stream" sparkle:edSignature="p72+LRQrBfOvNig7bQaYXSun0KKmjQ982LsmZpR/Z4QSwWJWHqyzIx4lWBWmiikhjwgR6Bu9jWB4eWtJjJQsDQ=="/>
+      <enclosure url="https://github.com/intitni/CopilotForXcode/releases/download/0.15.3/Copilot.for.Xcode.app.zip" length="21344856" type="application/octet-stream" sparkle:edSignature="p72+LRQrBfOvNig7bQaYXSun0KKmjQ982LsmZpR/Z4QSwWJWHqyzIx4lWBWmiikhjwgR6Bu9jWB4eWtJjJQsDQ=="/>
     </item>
 
     <item>