Fixed invalid parameter type in phpdoc block in Topmenu class

[vovayatsyuk]

Description

addIdentity method accepts strings, not an array.

See the usage:

1. https://github.com/magento/magento2/blob/2.2-develop/app/code/Magento/Catalog/Plugin/Block/Topmenu.php#L119
2. https://github.com/magento/magento2/blob/2.2-develop/app/code/Magento/Catalog/Plugin/Block/Topmenu.php#L129

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[dmanners]

technically this method accepts both strings and arrays as in_array will work with both and we never actually check the type. Since this class is noted with the @api I think it would be best to update the typehint to be string|array as we do not know how people use it.

[vovayatsyuk]

Thanks, never know that I can use array as identity.

[dmanners]

I mean technically you can, not sure you should do though.