Add missing import

src/HAB/Solr/Facet/Impl/FieldFacet.php

@@ -28,6 +28,7 @@ use HAB\Solr\Facet\Value\FacetValue;
 
 use HAB\Solr\Response\Json\RecordCollection;
 
+use Traversable;
 use InvalidArgumentException;
 
 /**
@@ -360,4 +361,4 @@ class FieldFacet implements FacetImplInterface
         }
         $this->fqTag = null;
     }
-}
\ No newline at end of file
+}