Write a function that accepts a string, and returns true if it is in the form of a phone number.
Assume that any integer from 0-9 in any of the spots will produce a valid phone number.
Only worry about the following format:
(123) 456-7890 (don't forget the space after the close parentheses)
Examples:
validPhoneNumber("(123) 456-7890") => returns true
validPhoneNumber("(1111)555 2345") => returns false
validPhoneNumber("(098) 123 4567") => returns false