Remove config names as yaml keys (#4367)

* validate YAML part

* fix bad YAML keys

* don't have config names as yaml keys

* style

* Remove hacking license tags when mirroring datasets on the Hub

* fix test

* fix style

* more fixes

* remove dots in QA column mapping keys

Commit from https://github.com/huggingface/datasets/commit/3f3013441e4af9bf4efa752b5e6e184a588b7a80

README.md

@@ -1,5 +1,5 @@
 ---
-pretty_name: SQuAD2-0
+pretty_name: SQuAD2.0
 annotations_creators:
 - crowdsourced
 language_creators:
@@ -7,7 +7,7 @@ language_creators:
 languages:
 - en
 licenses:
-- cc-by-sa-4-0
+- cc-by-sa-4.0
 multilinguality:
 - monolingual
 size_categories:
@@ -30,8 +30,8 @@ train-eval-index:
   col_mapping:
     question: question
     context: context
-    answers-text: answers-text
-    answers-answer_start: answers-answer_start
+    answers_text: answers.text
+    answers_start: answers.answer_start
   metrics:
   - type: squad_v2
     name: SQuAD v2