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

@@ -116,12 +116,12 @@ dataset_info:
   - name: domain
     dtype: string
   splits:
-  - name: train
-    num_bytes: 114778994
-    num_examples: 20431
   - name: validation
     num_bytes: 22705288
     num_examples: 3972
+  - name: train
+    num_bytes: 114778994
+    num_examples: 20431
   download_size: 5879543
   dataset_size: 137484282
 ---