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

@@ -33,12 +33,12 @@ dataset_info:
     dtype:
       class_label:
         names:
-          0: feat_snip
-          1: collection
-          2: knowledge
-          3: unit_conv
-          4: time_conv
-          5: curr_conv
+          '0': feat_snip
+          '1': collection
+          '2': knowledge
+          '3': unit_conv
+          '4': time_conv
+          '5': curr_conv
   splits:
   - name: train
     num_bytes: 974320061