code: public JenkinsServer updateJob(FolderJob folder, String jobName, String jobXml, boolean crumbFlag)
              throws IOException {
          client.post_xml(UrlUtils.toJobBaseUrl(folder, jobName) + "/config.xml", jobXml, crumbFlag);
          return this;
      }
docs: Update the xml description of an existing job
  
  @param folder the folder.
  @param jobName the name of the job.
  @param jobXml the job xml configuration.
  @param crumbFlag true/false.
  @throws IOException in case of an error.