updated maven version prerequisite from 2.0.6 to 2.2.1

git-svn-id: https://svn.apache.org/repos/asf/maven/doxia/doxia-tools/trunk@1730179 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/doxia-book-maven-plugin/pom.xml b/doxia-book-maven-plugin/pom.xml
index 115f831..e67c538 100644
--- a/doxia-book-maven-plugin/pom.xml
+++ b/doxia-book-maven-plugin/pom.xml
@@ -58,7 +58,7 @@
 
   <properties>
     <doxiaVersion>1.3</doxiaVersion>
-    <mavenVersion>2.0.6</mavenVersion>
+    <mavenVersion>2.2.1</mavenVersion>
     <pluginPluginVersion>3.1</pluginPluginVersion>
   </properties>