Fix error when asset pipeline isn't available
Fix error when asset pipeline isn't available

uswitch/premailer-rails,fphilipe/premailer-rails,controlshift/premailer-rails,controlshift/premailer-rails,fphilipe/premailer-rails,fphilipe/premailer-rails,controlshift/premailer-rails,doorkeeper/premailer-rails,doorkeeper/premailer-rails,uswitch/premailer-rails