champs mail unique

src/AppBundle/Entity/User.php

@@ -47,7 +47,7 @@ class User implements UserInterface
     /**
      * @var string
      *
-     * @ORM\Column(name="mail", type="string", length=255)
+     * @ORM\Column(name="mail", type="string", length=255, unique=true)
      */
     private $mail;