Change stop symbol to another one since chrome-win can't display it

web/react/components/file_attachment.jsx

@@ -187,7 +187,7 @@ export default class FileAttachment extends React.Component {
                     className='file-playback-controls stop'
                     onClick={(e) => this.stopGif(e, filename)}
                 >
-                    {"◼"}
+                    {"■"}
                 </div>
             );
         }

web/react/components/view_image.jsx

@@ -248,7 +248,7 @@ export default class ViewImageModal extends React.Component {
                                 className='file-playback-controls stop'
                                 onClick={(e) => this.stopGif(e, filename)}
                             >
-                                {"◼"}
+                                {"■"}
                             </div>
                         );
                     } else {