Write a method that takes in a String and returns a new
string that replaces every instance of the letters k, a, r, e, l with two occurrences of
that letter.

For example.

moreKarelLetters("kaleidoscope")

would return

"kkaaleeidoscopee"

Hint : Strings have a method .contains(str) which returns a boolean
indicating if a given Strings contains another String.