Write a function that takes three string arguments (first, last, and word) and returns true if word is found between first and last in the dictionary, otherwise false.
isBetween("apple", "banana", "azure") ➞ true
isBetween("monk", "monument", "monkey") ➞ true
isBetween("bookend", "boolean", "boost") ➞ false
word is in the middle.