Update maven-javadoc plugin to 3.2.0 (last to support Java 7)

Fixes a java.lang.ExceptionInInitializerError on Java 17 when running
`mvn package`, see #38 (comment)

Author: generalmimon

pom.xml

@@ -79,7 +79,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-javadoc-plugin</artifactId>
-        <version>2.9.1</version>
+        <version>3.2.0</version>
         <executions>
           <execution>
             <id>attach-javadocs</id>