phone: handle all digits to avoid TB

avoids traceback:

    phone.rb:24:in `join_sets': undefined method `each' for nil:NilClass (NoMethodError)
    from phone.rb:31:in `phone_options'
    from phone.rb:34:in `<main>'
phone: ignore non-digit characters in phone number, such as '-'.
Merge pull request #9 from jumanjiman/phone

Phone: avoid traceback when phone number contains 0 or 1