Create a function that takes an initial word and extracts any words that start with the same letters as the initial word.
dictionary("bu", ["button", "breakfast", "border"]) ➞ ["button"]
dictionary("tri", ["triplet", "tries", "trip", "piano", "tree"]) ➞ ["triplet", "tries", trip"]
dictionary("beau", ["pastry", "delicious", "name", "boring"]) ➞ []