Revert "Bump maven-javadoc-plugin from 3.1.1 to 3.2.0 (#1477)"

This reverts commit 7b199ff

The Javadoc aggregation got broken in 3.2.0 for EJB (nothing gets
written to target/site).

Author: dmitry-timofeev

exonum-java-binding/pom.xml

@@ -430,7 +430,7 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-javadoc-plugin</artifactId>
-          <version>3.2.0</version>
+          <version>3.1.1</version>
           <configuration>
             <source>${javadoc.source}</source>
             <doclint>none</doclint>

exonum-light-client/pom.xml

@@ -238,7 +238,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-javadoc-plugin</artifactId>
-        <version>3.2.0</version>
+        <version>3.1.1</version>
         <configuration>
           <source>${javadoc.source}</source>
           <doclint>none</doclint>