Update README.md

Use same license as original mnist dataset (due to SA clause)

README.md

@@ -1,14 +1,14 @@
 ---
-license: mit
+license: cc-by-sa-3.0
 task_categories:
-  - image-classification
+- image-classification
 language:
-  - en
+- en
 pretty_name: mnist_ambigous
 size_categories:
-  - 10K<n<100K
+- 10K<n<100K
 source_datasets:
-  - extended|mnist
+- extended|mnist
 annotations_creators:
-  - machine-generated
+- machine-generated
 ---