Pipe character (|) in domain is not blocked by PROHIBITED_DOMAIN_CHARACTERS_REGEX

`|` is not in `PROHIBITED_DOMAIN_CHARACTERS_REGEX`, so emails with a pipe in the domain incorrectly pass validation:

```ruby
ValidEmail2::Address.new("user@example.com|").valid?  # => true (should be false)
```

Per RFC 5321, domain labels only allow `[a-zA-Z0-9-]`. Adding `|` to the regex would fix this:

```ruby
PROHIBITED_DOMAIN_CHARACTERS_REGEX = /[+!_\/\s'`|]/
```