[ci-skip][doc] Fix typo in Validation Guides

Author: hachi8833

guides/source/active_record_validations.md

@@ -361,7 +361,7 @@ In modern Rails applications, the more concise validate syntax is commonly used,
 for example:
 
 ```ruby
-validate :name, presence: true
+validates :name, presence: true
 ```
 
 However, older versions of Rails used "helper" methods, such as: