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

@@ -67,12 +67,12 @@ dataset_info:
     sequence: string
   config_name: plain_text
   splits:
-  - name: test
-    num_bytes: 57712177
-    num_examples: 9633
   - name: train
     num_bytes: 4090681873
     num_examples: 516819
+  - name: test
+    num_bytes: 57712177
+    num_examples: 9633
   - name: validation
     num_bytes: 484107026
     num_examples: 58221