Update email field length in annotation

I believe 60 characters for email is not enough, because maximum length of email is 254 chars. See https://stackoverflow.com/a/574698/3000493

Author: Holicz

security/entity_provider.rst

@@ -70,7 +70,7 @@ For this entry, suppose that you already have a ``User`` entity inside an
         private $password;
 
         /**
-         * @ORM\Column(type="string", length=60, unique=true)
+         * @ORM\Column(type="string", length=254, unique=true)
          */
         private $email;