test: upgrade testbench-rpc to 1.4.0

Author: javier-godoy

pom.xml

@@ -122,7 +122,7 @@
         <dependency>
             <groupId>com.flowingcode.vaadin.test</groupId>
             <artifactId>testbench-rpc</artifactId>
-            <version>1.3.0</version>
+            <version>1.4.0</version>
         </dependency>
         <dependency>
             <groupId>com.flowingcode.vaadin.addons.demo</groupId>