add maven 3 prerequisites

pom.xml

@@ -37,6 +37,10 @@ THE SOFTWARE.
   
   <name>Jenkins main module</name>
   <description>The module that constitutes the main jenkins.war</description>
+
+  <prerequisites>
+    <maven>3.0</maven>
+  </prerequisites>
   
   <modules>
     <module>remoting</module>