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

@@ -37,12 +37,12 @@ dataset_info:
     - name: answer_start
       dtype: int32
   splits:
-  - name: test
-    num_bytes: 7858336
-    num_examples: 7609
   - name: train
     num_bytes: 50864824
     num_examples: 54159
+  - name: test
+    num_bytes: 7858336
+    num_examples: 7609
   download_size: 8776531
   dataset_size: 58723160
 ---