Excludes the xerces from rat-plugin dependency to avoid unrelated warning

- https://issues.apache.org/jira/browse/RAT-158 
diff --git a/pom.xml b/pom.xml
index acc9096..4eca415 100644
--- a/pom.xml
+++ b/pom.xml
@@ -249,6 +249,19 @@
                     <groupId>org.apache.rat</groupId>
                     <artifactId>apache-rat-plugin</artifactId>
                     <version>0.11</version>
+                    <dependencies>
+                        <dependency>
+                            <groupId>org.apache.maven.doxia</groupId>
+                            <artifactId>doxia-core</artifactId>
+                            <version>1.6</version>
+                            <exclusions>
+                                <exclusion>
+                                    <groupId>xerces</groupId>
+                                    <artifactId>xercesImpl</artifactId>
+                                </exclusion>
+                            </exclusions>
+                        </dependency>
+                    </dependencies>
                     <configuration>
                         <excludes>
                             <exclude>.git/**/*</exclude>