Create a function that, given a phrase and a number of letters guessed, returns a string with hyphens - for every letter of the phrase not guessed, and each letter guessed in place.
hangman("helicopter", ["o", "e", "s"]) ➞ "-e---o--e-"
hangman("tree", ["r", "t", "e"]) ➞ "tree"
hangman("Python rules", ["a", "n", "p", "r", "z"]) ➞ "P----n r----"
hangman("He"s a very naughty boy!", ["e", "a", "y"]) ➞ "-e"- a -e-y -a----y --y!"