Bump com.vaadin:vaadin-bom from 19.0.6 to 20.0.6

Bumps com.vaadin:vaadin-bom from 19.0.6 to 20.0.6.

---
updated-dependencies:
- dependency-name: com.vaadin:vaadin-bom
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

pom.xml

@@ -47,7 +47,7 @@
         <maven.compiler.target>1.8</maven.compiler.target>
         <failOnMissingWebXml>false</failOnMissingWebXml>
 
-        <vaadin.version>19.0.6</vaadin.version>
+        <vaadin.version>20.0.6</vaadin.version>
     </properties>
 
     <dependencyManagement>