Issue #3213539 by dshields: When using Migrate Plus, update the "Last imported" date stamp

<?php

/**

 * @file

 * Contains implementation of cron function to execute scheduled migrations.

          }

          $executable = new MigrateExecutable($migration, new MigrateMessage());

          $executable->import();

          // If using migrate_plus module, update the migrate_last_imported value for the migration.

          $moduleHandler = \Drupal::service('module_handler');

          if ($moduleHandler->moduleExists('migrate_plus')) {

            $migrate_last_imported_store = \Drupal::keyValue('migrate_last_imported');

            $migrate_last_imported_store->set($migration->id(), round(\Drupal::time()->getCurrentMicroTime() * 1000));

          }

        }

      }

    }