Write a function named validPasswords that examines a list of passwords and password policies and returns how many of the passwords are acceptable by those policies.
Your function accepts a string parameter representing a file name as a parameter.
Each line of the file contains a policy followed by a password.
A policy is of the form MIN-MAX LETTER indicating that the given letter must occur MIN to MAX number of times in the password, inclusive.
For example, if the file named passwords.txt contains the following values:
1-3 a: abcde
1-3 b: cdefg
2-9 c: ccccccccc
For example, 1-3 a means that the password must contain a at least 1 time and at most 3 times.
In the above example, 2 passwords are valid.
The middle password, cdefg, is not; it contains no instances of b, but needs at least 1.
The first and third passwords are valid: they contain one a or nine c, both within the limits of their respective policies.
So the call of validPasswords("passwords.txt") should return 2.
You may assume that the file exists and is readable and that it follows the format described above.
NOTE: You can read the entire contents of a file as a string by calling fs.readFileSync(filename).
