Do not filter out scopes from Ransack queries

Scopes are special in that they don't have a predicate. This removes the
check for the predicate, and thus makes scopes as filtering options work
with JSONAPI.rb.

Author: mamhoff

lib/jsonapi/filtering.rb

@@ -62,7 +62,7 @@ def jsonapi_filter_params(allowed_fields)
           to_filter = to_filter.split(',')
         end
 
-        if predicates.any? && (field_names - allowed_fields).empty?
+        if (field_names - allowed_fields).empty?
           filtered[requested_field] = to_filter
         end
       end

spec/dummy.rb

@@ -32,7 +32,7 @@
 class User < ActiveRecord::Base
   has_many :notes
 
-  scope :created_before, ->(date) { where("created_at < ?", date) }
+  scope :created_before, ->(date) { where('created_at < ?', date) }
 
   def self.ransackable_scopes(_auth_object = nil)
     [:created_before]