use invoker plugin 1.8 which correctly ignore .gitignore files when cloning projects

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1447055 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index 23b88b7..64d98c7 100644
--- a/pom.xml
+++ b/pom.xml
@@ -189,6 +189,7 @@
           <plugin>
             <groupId>org.apache.maven.plugins</groupId>
             <artifactId>maven-invoker-plugin</artifactId>
+            <version>1.8</version>
             <configuration>
               <projectsDirectory>src/it</projectsDirectory>
               <cloneProjectsTo>${project.build.directory}/it</cloneProjectsTo>