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

@@ -108,10 +108,10 @@ A typical data point comprises a `question`, it's `answer` the `language` of the
 
 The data is split into a training, validation and test set for each of the two configurations.
 
-|                            | Tain   | Valid | Test |
-| -----                      | ------ | ----- | ---- |
-| XOR Retrieve               |   15250|   2113|  2501|
-| XOR Full                   |   61360|   3179|  8177|
+|              | train | validation | test |
+|--------------|------:|-----------:|-----:|
+| XOR Retrieve | 15250 |       2113 | 2501 |
+| XOR Full     | 61360 |       3179 | 8177 |
 
 ## Dataset Creation