Bumped up the maven-site plugin to 3.5.1

git-svn-id: https://svn.apache.org/repos/asf/directory/project/trunk@1767525 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/pom.xml b/pom.xml
index e5cb481..f3b5c23 100644
--- a/pom.xml
+++ b/pom.xml
@@ -772,7 +772,7 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-site-plugin</artifactId>
-          <version>3.4</version>
+          <version>3.5.1</version>
         </plugin>
 
         <plugin>