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

@@ -69,12 +69,12 @@ dataset_info:
       sequence: float32
   config_name: plain_text
   splits:
-  - name: test
-    num_bytes: 3327158
-    num_examples: 1107
   - name: train
     num_bytes: 26979472
     num_examples: 8967
+  - name: test
+    num_bytes: 3327158
+    num_examples: 1107
   - name: validation
     num_bytes: 3267881
     num_examples: 1083