Bug with Numbers being interrupted by alpha chars [a-z]

``` js
format('(###)###-####',  "9166163a600" )
format('(000)000-0000', "9166163a600" )
```

Produces:

``` js
AssertionError: '(916)616-3' == '(916)616-3600'
      + expected - actual

      - (916)616-3
      + (916)616-3600
```
