Fix links to xhtml files

src/index.html

@@ -25,7 +25,7 @@
         </div>
 
         <div id="navbar"><div id="navbar-inner">
-            <a href="index.xhtml" class="active">Home</a>
+            <a href="index.html" class="active">Home</a>
         </div></div>
 
         <div id="main">
@@ -44,7 +44,7 @@
                 <h2>Contact</h2>
                 <ul>
                     <li><b>Mail:</b> <a href="res/mail.png">Link to graphic with address</a></li>
-                    <li><b>Matrix messenger:</b> @eisfunke:eisfunke.com (<a href="matrix.xhtml">Device keys</a>)</li>
+                    <li><b>Matrix messenger:</b> @eisfunke:eisfunke.com (<a href="matrix.html">Device keys</a>)</li>
                     <li><b>Telegram messenger:</b> @Eisfunke</li>
                     <li><b>Signal messenger:</b> Available</li>
                     <li><b>Briar messenger:</b> Available</li>

src/matrix.html

@@ -26,7 +26,7 @@
 
         <div id="navbar">
             <div>
-                <a href="index.xhtml">HOME</a>
+                <a href="index.html">HOME</a>
             </div>
         </div>