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

@@ -134,10 +134,10 @@ The original splits were named `train`, `testa` and `testb` and they correspond
 
 The splits have the following sizes :
 
-|                            | Tain   | Valid | Test |
-| -----                      | ------ | ----- | ---- |
-| N. Examples (Spanish)      | 8324   | 1916  | 1518 |
-| N. Examples (Dutch)        | 15807  | 2896  | 5196 |
+|                            |  train |  validation |  test |
+| -----                      |-------:|------------:|------:|
+| N. Examples (Spanish)      |   8324 |        1916 |  1518 |
+| N. Examples (Dutch)        |  15807 |        2896 |  5196 |
 
 ## Dataset Creation