use correct method name

src/JsonFieldRequirements.php

@@ -43,7 +43,7 @@ class JsonFieldRequirements implements JsonFieldRequirementsInterface {
     $exists = file_exists($this->root . $library_paths[0]) && file_exists($this->root . $library_paths[1]) ? TRUE : FALSE;
     if (!$exists) {
       if ($warning) {
-        $this->messenger()->addWarning($this->getWarningMessage());
+        $this->messenger()->addWarning($this->getLibraryWarningMessage());
       }
 
       return FALSE;