Fixed typo in class name.

Clicking "Check for orphans" on admin/config/capx/importer leads to
 
 Fatal error: Class 'CAPx\Drupal\Importer\Orphans\Comparisons\CompareMissingFromApi' not found in stanford_capx/includes/CAPx/Drupal/Util/CAPxImporter.php on line 170.