Update Tests.elm
Update Tests.elm

The format of _NANP_ phone numbers is described in the [README](https://github.com/exercism/elm/edit/master/exercises/phone-number/README.md) as 

`````
(NXX)-NXX-XXXX
`````

where `N` is a digit from 2 through 9, but all the tests for valid phone numbers test for `Just "1234567890"`.
That means the first digit of the _area code_, `N`, would be 1 there every time, for which a correct implementation should return `Nothing`.

My change would simply increment those 1s to 2, as i believe the intention is to test for valid numbers here.

Additionally I introduced two new test cases, expecting `Nothing`, when either digit `N` in the format is equal to 1.
exercism/xelm