feat: implement Serializable

Author: ngonzalezpazFC

src/main/java/com/flowingcode/vaadin/addons/simpletimer/SimpleTimer.java

@@ -35,13 +35,14 @@
 import com.vaadin.flow.component.dependency.JsModule;
 import com.vaadin.flow.dom.PropertyChangeListener;
 import com.vaadin.flow.shared.Registration;
+import java.io.Serializable;
 
 /**
  * @author Leonardo Scardanzan / Flowing Code
  */
 @Tag("simple-timer")
 @JsModule("./simple-timer/simple-timer.js")
-public class SimpleTimer extends Component implements HasSize, HasStyle {
+public class SimpleTimer extends Component implements HasSize, HasStyle, Serializable {
 
 	private static final long serialVersionUID = 1L;