Fix typo in validations documentation. Closes #7669. [ee]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6301 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/lib/active_record/validations.rb

@@ -452,10 +452,10 @@ def validates_acceptance_of(*attr_names)
       # === Warning
       # Validate the presence of the foreign key, not the instance variable itself.
       # Do this:
-      #  validate_presence_of :invoice_id
+      #  validates_presence_of :invoice_id
       #
       # Not this:
-      #  validate_presence_of :invoice
+      #  validates_presence_of :invoice
       #
       # If you validate the presence of the associated object, you will get
       # failures on saves when both the parent object and the child object are