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

@@ -87,9 +87,9 @@ A typical data point comprises a rating from 1 to 5 where the higher the rating
 
 The data is split into a training and testing. The split is organized as the following 
 
-|           | Tain   | Test |
-|---------- | ------ | ---- |
-|data split | 11,760 | 2,935|
+|           |  train |  test |
+|---------- |-------:|------:|
+|data split | 11,760 | 2,935 |
 
 ## Dataset Creation