Highlight has_rich_text

Closes tpope#576

Author: tpope

after/syntax/ruby/rails.vim

@@ -42,7 +42,7 @@ elseif s:path =~# '/app/models/.*\.rb$'
   syn keyword rubyCallback after_find after_initialize after_touch
   syn keyword rubyValidation validates 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_with
   syn keyword rubyValidation validates_associated validates_uniqueness_of
-  syn keyword rubyMacro validate has_secure_password has_secure_token has_one_attached has_many_attached
+  syn keyword rubyMacro validate has_rich_text has_secure_password has_secure_token has_one_attached has_many_attached
 endif
 
 if s:path =~# '/app/jobs/.*\.rb$'