Change validate to validates for validating repo name

 - validate is used for custom validation but Rails > 4.2 does not
   complain even if we accidently call it with validates options.
 - Rails 4.2 has raises exception that uniqueness option is not accepted
   by `validate` method.
 - This looks like a typo where we wanted to call `validates`.
 - Also removed a duplicate instance of `validates` which was validating
   repo name again.