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

@@ -43,11 +43,11 @@ dataset_info:
       dtype:
         class_label:
           names:
-            0: Coverall
-            1: Face_Shield
-            2: Gloves
-            3: Goggles
-            4: Mask
+            '0': Coverall
+            '1': Face_Shield
+            '2': Gloves
+            '3': Goggles
+            '4': Mask
   splits:
   - name: train
     num_bytes: 240481281