Update appcast.xml

Author: sbarex

appcast.xml

@@ -15,7 +15,7 @@
             />
             <description><![CDATA[
                 <h2>Release 2.1.23 (72)</h2>
-                <p align="right">If you like this app, <a href="https://www.buymeacoffee.com/sbarex">buy me a coffee!</a></p>
+                <p align="center">If you like this app, <a href="https://www.buymeacoffee.com/sbarex">buy me a coffee!</a></p>
                 <p>New features:</p>
                 <ul>
                     <li>Update Highlight to release 4.12.</li>