Fix typo in train split name (#3751)

* Fix typo in README guide

* Fix split naming and table alignment in README guide

* Fix split naming and table alignment in all datasets

* Fix previously malformed dataset cards

* Fix previously malformed dataset cards

Commit from https://github.com/huggingface/datasets/commit/af6e54febe3b822118dfed28ddb797d8350e5d27

README.md

@@ -101,9 +101,9 @@ Each MR consists of 3–8 attributes (slots), such as name, food or area, and th
 
 The dataset is split into training, validation and testing sets (in a 76.5-8.5-15 ratio), keeping a similar distribution of MR and reference text lengths and ensuring that MRs in different sets are distinct.
 
-|                            | Tain   | Valid | Test |
-| -----                      | ------ | ----- | ---- |
-| N. Instances               | 33525  | 4299  | 4693 |
+|              | train | validation | test |
+|--------------|------:|-----------:|-----:|
+| N. Instances | 33525 |       4299 | 4693 |
 
 ## Dataset Creation