Validate user email syntax on change

We probably have invalid entries in the database and we don't want these
records to suddenly become invalid. People would not be able to log in.

app/models/spree/user.rb

@@ -48,6 +48,7 @@ module Spree
 
     after_create :associate_customers, :associate_orders
 
+    validates :email, 'valid_email_2/email': true, if: :email_changed?
     validate :limit_owned_enterprises
     validates :uid, uniqueness: true, if: lambda { uid.present? }
     validates_email :uid, if: lambda { uid.present? }

spec/models/spree/user_spec.rb

@@ -92,7 +92,7 @@ describe Spree::User do
       expect(user.errors.messages[:email]).to include "is invalid"
     end
 
-    pending "detects backslashes at the end" do
+    it "detects backslashes at the end" do
       user.email = "example@gmail.com\\\\"
       expect(user).to_not be_valid
     end