Explicitly sign artifacts in verify phase (#3201)

When no phase is specified some of the artifacts are signed too late
Ref https://github.com/Activiti/Activiti/issues/3184

pom.xml

@@ -730,6 +730,7 @@
             <executions>
               <execution>
                 <id>sign-artifacts</id>
+                <phase>verify</phase>
                 <goals>
                   <goal>sign</goal>
                 </goals>