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

@@ -48,12 +48,12 @@ dataset_info:
     dtype: string
   config_name: atomic
   splits:
-  - name: test
-    num_bytes: 3995624
-    num_examples: 24856
   - name: train
     num_bytes: 32441878
     num_examples: 202271
+  - name: test
+    num_bytes: 3995624
+    num_examples: 24856
   - name: validation
     num_bytes: 3629768
     num_examples: 22620