minor #9402 Update email field length in annotation (User class in security section) (Holicz)

This PR was submitted for the 4.0 branch but it was merged into the 2.7 branch instead (closes #9402).

Discussion
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Update email field length in annotation (User class in security section)

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

Commits
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8324c93 Update email field length in annotation

Author: javiereguiluz

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;