Write a program that converts a number to a string per the following rules:
If the number contains 3 as a prime factor, output 'Pling'. If the number contains 5 as a prime factor, output 'Plang'. If the number contains 7 as a prime factor, output 'Plong'.
If the number does not contain 3, 5, or 7 as a prime factor, simply return the string representation of the number itself.
E.g.
The prime factors of 28 are [2, 2, 7].
drops = Raindrops.new.convert(28)
# => "Plong"The prime factors of 1755 are [3, 3, 3, 5, 13].
drops = Raindrops.new.convert(1755)
# => "PlingPlang"The prime factors of 34 are [2, 17].
drops = Raindrops.new.convert(34)
# => "34"