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

@@ -39,12 +39,12 @@ dataset_info:
           9: Ankle boot
   config_name: fashion_mnist
   splits:
-  - name: test
-    num_bytes: 5233818
-    num_examples: 10000
   - name: train
     num_bytes: 31296655
     num_examples: 60000
+  - name: test
+    num_bytes: 5233818
+    num_examples: 10000
   download_size: 30878645
   dataset_size: 36530473
 ---