HADOOP-14056. Update maven-javadoc-plugin to 2.10.4.

hadoop-project/pom.xml

@@ -1322,7 +1322,7 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-javadoc-plugin</artifactId>
-          <version>2.8.1</version>
+          <version>${maven-javadoc-plugin.version}</version>
           <configuration>
             <additionalparam>-Xmaxwarns 10000</additionalparam>
           </configuration>

pom.xml

@@ -98,7 +98,7 @@ xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xs
     <maven-assembly-plugin.version>2.4</maven-assembly-plugin.version>
     <maven-dependency-plugin.version>2.10</maven-dependency-plugin.version>
     <maven-enforcer-plugin.version>1.4.1</maven-enforcer-plugin.version>
-    <maven-javadoc-plugin.version>2.9.1</maven-javadoc-plugin.version>
+    <maven-javadoc-plugin.version>2.10.4</maven-javadoc-plugin.version>
     <maven-gpg-plugin.version>1.5</maven-gpg-plugin.version>
     <maven-remote-resources-plugin.version>1.5</maven-remote-resources-plugin.version>
     <maven-resources-plugin.version>3.0.1</maven-resources-plugin.version>