MNEMONIC-539: Javadoc generation on openJDK 11 issue

Signed-off-by: Gary <garyw@apache.org>
diff --git a/pom.xml b/pom.xml
index e812906..886df0f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -389,7 +389,10 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-javadoc-plugin</artifactId>
-          <version>2.10.3</version>
+          <version>3.2.0</version>
+          <configuration>
+            <source>8</source>
+          </configuration>
         </plugin>
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>