Restored some PHP 7.4 support

src/Dataset.php

@@ -116,11 +116,21 @@ class Dataset
             return $reader;
         }
         $ext = pathinfo($filename, PATHINFO_EXTENSION);
+
+        /*
         return match ($ext) {
             'json' => JsonReader::class,
             'csv' => CsvReader::class,
             default => throw new \RuntimeException("Unable to determine reader for dataset file")
         };
+        */
+
+        // PHP7.4 compat: use switch instead of match
+        switch ($ext) {
+            case 'json': return JsonReader::class;
+            case 'csv': return CsvReader::class;
+            default: throw new \RuntimeException("Unable to determine reader for dataset file");
+        }
     }
     
-}
+}