Fixes missing context on show_related_resources

Fixes #763

Author: lgebhardt

lib/jsonapi/processor.rb

@@ -148,6 +148,7 @@ def show_related_resources
       source_resource ||= source_klass.find_by_key(source_id, context: context, fields: fields)
 
       related_resources = source_resource.public_send(relationship_type,
+                                                      context: context,
                                                       filters:  filters,
                                                       sort_criteria: sort_criteria,
                                                       paginator: paginator,

test/fixtures/active_record.rb

@@ -662,12 +662,21 @@ class BreedsController < JSONAPI::ResourceController
     end
 
     class PlanetsController < JSONAPI::ResourceController
+      def context
+        {current_user: $test_user}
+      end
     end
 
     class PlanetTypesController < JSONAPI::ResourceController
+      def context
+        {current_user: $test_user}
+      end
     end
 
     class MoonsController < JSONAPI::ResourceController
+      def context
+        {current_user: $test_user}
+      end
     end
 
     class CratersController < JSONAPI::ResourceController