Send emails to current budget authors in rake tasks

We were using `Budget.last`, but the last budget might not be published
yet.

I must admit I don't know whether these tasks are useful, but I'm not
removing them because I'm not sure that won't harm any CONSUL
installations.

lib/tasks/budgets.rake

@@ -2,12 +2,12 @@ namespace :budgets do
   namespace :email do
     desc "Sends emails to authors of selected investments"
     task selected: :environment do
-      Budget.last.email_selected
+      Budget.current.email_selected
     end
 
     desc "Sends emails to authors of unselected investments"
     task unselected: :environment do
-      Budget.last.email_unselected
+      Budget.current.email_unselected
     end
   end
 end