[mirotalksfu] - improve open Nav

public/view/Room.html

@@ -96,7 +96,7 @@ access to use this app.
             </pre>
         </div>
 
-        <button id="openNavButton" class="hidden">&#9776; menu</button>
+        <button id="openNavButton" class="hidden">&#9776;</button>
         <div id="control" class="sidenav hidden">
             <button id="closeNavButton" class="closebtn">&times;</button>
             <button id="shareButton" class="hidden"><i class="fas fa-share-alt"></i> Share</button>