Correct version name of site plugin.

pom.xml

@@ -380,7 +380,7 @@
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-site-plugin</artifactId>
-				<version>2.0-BETA-5</version>
+				<version>2.0-beta-5</version>
 			</plugin>
             <plugin>
                 <groupId>com.agilejava.docbkx</groupId>