code: public Observable<Page<CertificateItem>> getCertificateVersionsAsync(final String vaultBaseUrl, final String certificateName, final Integer maxresults) {
          return getCertificateVersionsWithServiceResponseAsync(vaultBaseUrl, certificateName, maxresults)
              .map(new Func1<ServiceResponse<Page<CertificateItem>>, Page<CertificateItem>>() {
                  @Override
                  public Page<CertificateItem> call(ServiceResponse<Page<CertificateItem>> response) {
                      return response.body();
                  }
              });
      }
docs: List the versions of a certificate.
  The GetCertificateVersions operation returns the versions of a certificate in the specified key vault. This operation requires the certificates/list permission.
  
  @param vaultBaseUrl The vault name, for example https://myvault.vault.azure.net.
  @param certificateName The name of the certificate.
  @param maxresults Maximum number of results to return in a page. If not specified the service will return up to 25 results.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the PagedList&lt;CertificateItem&gt; object