Use ActiveRecord::Relation#count with a block

This method used to ignore the block but in Rails 5.1 it uses
Enumerable#count.

See https://github.com/rails/rails/pull/24203/commits/58772397

app/controllers/valuation/budget_investments_controller.rb

@@ -87,7 +87,7 @@ class Valuation::BudgetInvestmentsController < Valuation::BaseController
         filters << {
                      name: heading.name,
                      id: heading.id,
-                     count: investments.select { |i| i.heading_id == heading.id }.size
+                     count: investments.count { |i| i.heading_id == heading.id }
                    }
       end
     end