Add validates_absence_of to AR highlighting

Added in autoload/rails.vim

Author: eljojo

autoload/rails.vim

@@ -3770,7 +3770,7 @@ function! rails#buffer_syntax()
         syn keyword rubyRailsARCallbackMethod around_create around_destroy around_save around_update
         syn keyword rubyRailsARCallbackMethod after_commit after_find after_initialize after_rollback after_touch
         syn keyword rubyRailsARClassMethod attr_accessible attr_protected attr_readonly has_secure_password store_accessor
-        syn keyword rubyRailsARValidationMethod validate validates validate_on_create validate_on_update validates_acceptance_of validates_associated validates_confirmation_of validates_each validates_exclusion_of validates_format_of validates_inclusion_of validates_length_of validates_numericality_of validates_presence_of validates_size_of validates_uniqueness_of validates_with
+        syn keyword rubyRailsARValidationMethod validate validates validate_on_create validate_on_update validates_acceptance_of validates_associated validates_confirmation_of validates_each validates_exclusion_of validates_format_of validates_inclusion_of validates_length_of validates_numericality_of validates_presence_of validates_absence_of validates_size_of validates_uniqueness_of validates_with
         syn keyword rubyRailsMethod logger
       endif
       if buffer.type_name('model-observer')