Add new Archetype for vaadin 7.5.9 with Java 8

Hi,
I have added a new archetype for new vaadin release 7.5.9 .
Now my pom looks like:

<properties>
<vaadin.version>7.5.9</vaadin.version>
<vaadin.plugin.version>${vaadin.version}</vaadin.plugin.version>
<jetty.plugin.version>9.2.3.v20140905</jetty.plugin.version>
<project.source.version>1.7</project.source.version>
<project.target.version>1.7</project.target.version>
<project.encoding>UTF-8</project.encoding>
</properties>

How can set the pom to use java 1.8 instead of 1.7? I know i can just change the value in pom, but is there a way to set
this as a fixed value, so that after creating a new vaadin maven project, the values for source and target versions are 1.8 by default?
regards
Iman