popup: Replace deprecated icon

Author: tchx84

src/popup.ui

@@ -28,7 +28,7 @@
             <property name="valign">center</property>
             <child>
               <object class="GtkImage">
-                <property name="icon-name">emblem-ok-symbolic</property>
+                <property name="icon-name">object-select-symbolic</property>
               </object>
             </child>
           </object>