Change as: proc to be run in the context of the entity.

Author: James McCarthy

lib/grape_entity/exposure/base.rb

@@ -104,7 +104,7 @@ def attr_path(entity, options)
         end
 
         def key(entity = nil)
-          @key.respond_to?(:call) ? @key.call(entity) : @key
+          @key.respond_to?(:call) ? entity.exec_with_object(@options, &@key) : @key
         end
 
         def with_attr_path(entity, options)

spec/grape_entity/exposure_spec.rb

@@ -33,7 +33,7 @@
     end
 
     it 'returns the result if :as is a proc' do
-      fresh_class.expose :name, as: -> (entity) { entity.object.name.reverse }
+      fresh_class.expose :name, as: -> { object.name.reverse }
       expect(subject.key(entity)).to eq(model.name.reverse)
     end
   end