Fix typo in config_description hash key
Fix typo in config_description hash key

Typo “seriserialization_options” → “serialization_options”. I couldn't find any references to this misspelt key in the current codebase, neither any GitHub search result besides forks of jsonapi-resources 😄 So I presume it's safe to correct it.

The only usage of the affected `config_description` method I found ends up using the keys as [part of a cache key](https://github.com/cerebris/jsonapi-resources/blob/d87cd2d2e80ab7660081c32db2303f196860b060/lib/jsonapi/resource_set.rb#L28), which won't be affected either.
cerebris/jsonapi-resources