Reorder split names

Reorder split names in the YAML metadata to be aligned with the order in the loading script.
See: https://github.com/huggingface/datasets/issues/5258

README.md

@@ -49,15 +49,15 @@ dataset_info:
     dtype: int32
   config_name: quail
   splits:
-  - name: challenge
-    num_bytes: 1199840
-    num_examples: 556
   - name: train
     num_bytes: 23432697
     num_examples: 10246
   - name: validation
     num_bytes: 4989579
     num_examples: 2164
+  - name: challenge
+    num_bytes: 1199840
+    num_examples: 556
   download_size: 6402933
   dataset_size: 29622116
 ---