phone number: only one problem per test input (#1959)
phone number: only one problem per test input (#1959)

* [Phone Number] Only one problem per test input

Because the area code is not allowed to start with 0 or 1, inputs designed to elicit other errors should not use area codes that start with either of those digits.

* Respect immutability

* Correct field name: s/comment/comments/

* Comments should contain a list.

* Allow prettier to improve comments
jmluy/x-common,exercism/x-common,jmluy/x-common,exercism/x-common,jmluy/x-common