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

@@ -32,12 +32,12 @@ dataset_info:
           0: negative
           1: positive
   splits:
-  - name: test
-    num_bytes: 5491417
-    num_examples: 50000
   - name: train
     num_bytes: 16423803
     num_examples: 150000
+  - name: test
+    num_bytes: 5491417
+    num_examples: 50000
   download_size: 19522142
   dataset_size: 21915220
 ---