upgrade invoker plugin

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1096556 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index fcb2203..5e21de7 100644
--- a/pom.xml
+++ b/pom.xml
@@ -148,7 +148,6 @@
           <plugin>
             <groupId>org.apache.maven.plugins</groupId>
             <artifactId>maven-invoker-plugin</artifactId>
-            <version>1.4</version>
             <configuration>
               <debug>true</debug>
               <projectsDirectory>src/it</projectsDirectory>