specify <source> for maven-javadoc-plugin so generating javadoc on JDK11+ does not complain about lack of java module declarations

Author: mikesamuel

parent/pom.xml

@@ -151,7 +151,7 @@ application while protecting against XSS.
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-javadoc-plugin</artifactId>
-          <version>3.1.1</version>
+          <version>3.2.0</version>
           <executions>
             <execution>
               <id>attach-javadocs</id>
@@ -176,6 +176,7 @@ application while protecting against XSS.
                 <value>bar</value>
               </property>
             </javaApiLinks>
+            <source>6</source>
           </configuration>
         </plugin>
         <plugin>