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

@@ -56,12 +56,12 @@ dataset_info:
           1: '2'
   config_name: plain_text
   splits:
-  - name: test
-    num_bytes: 27962097
-    num_examples: 38000
   - name: train
     num_bytes: 413558837
     num_examples: 560000
+  - name: test
+    num_bytes: 27962097
+    num_examples: 38000
   download_size: 166373201
   dataset_size: 441520934
 ---