Replace YAML keys from int to str

Replace YAML metadata integer keys with strings, as the Hub does not support integers.
See: https://github.com/huggingface/datasets/issues/5275

README.md

@@ -27,10 +27,10 @@ dataset_info:
     dtype:
       class_label:
         names:
-          0: others
-          1: happy
-          2: sad
-          3: angry
+          '0': others
+          '1': happy
+          '2': sad
+          '3': angry
   config_name: emo2019
   splits:
   - name: train