Fix javadocs under java 8

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@1806582 13f79535-47bb-0310-9956-ffa450edef68

pom.xml

@@ -61,6 +61,17 @@
   <build>
     <pluginManagement>
       <plugins>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-javadoc-plugin</artifactId>
+          <configuration>
+            <tags>
+              <tag>
+                <name>event.severity</name>
+              </tag>
+            </tags>
+          </configuration>
+        </plugin>
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-checkstyle-plugin</artifactId>