fix javadoc

Author: alexcheng1982

pom.xml

@@ -118,7 +118,7 @@
             <version>1.9.20</version>
             <configuration>
               <sourceDirectories>
-                <dir>${project.basedir}/src/main/kotlin</dir>
+                <dir>${project.basedir}/src/main/java</dir>
               </sourceDirectories>
             </configuration>
             <executions>