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

@@ -34,12 +34,12 @@ dataset_info:
           4: '5'
   config_name: plain_text
   splits:
-  - name: test
-    num_bytes: 1703399
-    num_examples: 2935
   - name: train
     num_bytes: 7051103
     num_examples: 11760
+  - name: test
+    num_bytes: 1703399
+    num_examples: 2935
   download_size: 39953712
   dataset_size: 8754502
 ---