Add missing references to BudgetItem scopes

Signed-off-by: Alex Coles <alex@alexbcoles.com>

app/models/labor_budget_item.rb

@@ -42,6 +42,7 @@ class LaborBudgetItem < ActiveRecord::Base
   scope :visible_costs, lambda{|*args|
     includes([{ cost_object: :project }, :user])
       .where(LaborBudgetItem.visible_condition((args.first || User.current), args[1]))
+      .references(:projects)
   }
 
   def costs

app/models/material_budget_item.rb

@@ -35,6 +35,7 @@ class MaterialBudgetItem < ActiveRecord::Base
   scope :visible_costs, lambda { |*args|
     where(MaterialBudgetItem.visible_condition((args.first || User.current), args[1]))
       .includes(cost_object: :project)
+      .references(:projects)
   }
 
   def costs