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

@@ -33,17 +33,17 @@ dataset_info:
     dtype:
       class_label:
         names:
-          0: 'no'
-          1: 'yes'
+          '0': 'no'
+          '1': 'yes'
   - name: category
     dtype:
       class_label:
         names:
-          0: Event Duration
-          1: Event Ordering
-          2: Frequency
-          3: Typical Time
-          4: Stationarity
+          '0': Event Duration
+          '1': Event Ordering
+          '2': Frequency
+          '3': Typical Time
+          '4': Stationarity
   config_name: plain_text
   splits:
   - name: test