fix(serializer): attributes with hashes as values ending up without camelCase keys in Rails

In Rails, doing

```
WebAuthn::Credential.options_for_create(user: { name: 'john', id: WebAuthn.generate_user_id }, authenticator_selection: { user_verification: "required" }).as_json
```

results in:

```
{:challenge=>"QVFtcdn_znYUWzAzmBSGpOPWweTs1tBmqPQENeGjUvA",
 :timeout=>120000,
 :extensions=>{},
 :rp=>{:name=>"WebAuthn Rails Demo App"},
 :user=>{:name=>"john", :id=>"8kzxeLCJ13lE5g7T7pE0TxCRxy_4Mcpp1lWS6geXJAiz7rPXHOWSJy_Ou33GP7lCvn_u5uIhDZzOez_cWoMGcA", :displayName=>"john"},
 :pubKeyCredParams=>[{"type"=>"public-key", "alg"=>-7}, {"type"=>"public-key", "alg"=>-37}, {"type"=>"public-key", "alg"=>-257}],
 :authenticatorSelection=>{"user_verification"=>"required"}}
```

(Notice the `user_verification` key under `authenticatorSelection`
without being camelCased)

This causes errors with some authenticators – particularly with
1Password.

The issue is that for the attributes whose value is a hash – as in
Rails, hash objects respond to `as_json` – are not going through the
part of the condition that calls camelCases its keys.

To fix this, this commit attempts to go back at the initial approach -
before 0aab124 – that first converts the object into a hash and then
camel cases its keys, even though more iterations are performed on the
object.

Author: santiagorodriguez96

lib/webauthn/json_serializer.rb

@@ -4,19 +4,21 @@ module WebAuthn
   module JSONSerializer
     # Argument wildcard for Ruby on Rails controller automatic object JSON serialization
     def as_json(*)
-      to_hash_with_camelized_keys
+      deep_camelize_keys(to_hash)
     end
 
     private
 
-    def to_hash_with_camelized_keys
+    def to_hash
       attributes.each_with_object({}) do |attribute_name, hash|
         value = send(attribute_name)
 
-        if value && value.respond_to?(:as_json)
-          hash[camelize(attribute_name)] = value.as_json
-        elsif value
-          hash[camelize(attribute_name)] = deep_camelize_keys(value)
+        if value.respond_to?(:as_json)
+          value = value.as_json
+        end
+
+        if value
+          hash[attribute_name] = value
         end
       end
     end