build: update vaadin version to 14.8.1

Author: paodb

pom.xml

@@ -9,7 +9,7 @@
     <description>Simple Timer for Vaadin Flow</description>
 
     <properties>
-        <vaadin.version>14.4.0</vaadin.version>
+        <vaadin.version>14.8.1</vaadin.version>
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>