FIX code review

app/services/gitea/user/register_service.rb

@@ -1,4 +1,5 @@
 class Gitea::User::RegisterService < Gitea::ClientService
+  API_REST = "/admin/users"
   def initialize(options = {})
     options.each_pair do |key, value|
       instance_variable_set("@#{key}", value)
@@ -6,15 +7,14 @@ class Gitea::User::RegisterService < Gitea::ClientService
   end
 
   def call
-    url = "/admin/users"
     params = {}
     params = params.merge(data: user_params)
-    post(url, params)
+    post(API_REST, params)
   end
 
   private
 
-  attr_reader :email, :username, :password, :url
+  attr_reader :email, :username, :password
 
   def user_params
     {