Referral email should be case_insensitive

[jwjwyoung]

ror_ecommerce/app/models/referral.rb

Line 10 in 3db5a29

validates :email, presence: true,

with current validation code, I can create referrals with same email adrress with lowercase/uppercase as attached.

I believe here should use
validates :email, presence: true, uniqueness: {case_sensitive: false}, format: { with: CustomValidators::Emails.email_validator }