Fix #930: only dup StackableValues.

Author: Todd Mazierski

lib/grape/util/stackable_values.rb

@@ -45,7 +45,7 @@ def freeze_value(key)
       def initialize_copy(other)
         super
         self.inherited_values = other.inherited_values
-        self.new_values = other.new_values.deep_dup
+        self.new_values = other.new_values.dup
       end
     end
   end

spec/grape/util/stackable_values_spec.rb

@@ -109,6 +109,16 @@ module Util
 
           expect(grandchild.clone.to_hash).to eq(some_thing: [:foo, [:bar, :more], :grand_foo_bar], some_thing_more: [:foo_bar])
         end
+
+        context 'complex (i.e. not primitive) data types (ex. middleware, please see bug #930)' do
+          let(:middleware) { double }
+
+          before { subject[:middleware] = middleware }
+
+          it 'copies values; does not duplicate them' do
+            expect(obj_cloned[:middleware]).to eq [middleware]
+          end
+        end
       end
     end
   end