Update rotate_pairs.py

[DavidVFitzGerald]

The current solution does not check for all rotated words, due to the stop argument of the range being 14 instead of 26 in the rotate_pairs function. For example, the word "act" should print out "act 24 yar", but currently does not print out anything.

As the current solution uses a somewhat brute force approach, my suggested solution uses a different approach, where each word is rotated only once. It also makes use of a dictionary to store the rotate pairs, by using the setdefault method covered in Exercise 11.2.

This suggested solution also directly addresses the specification of the exercise description ("Write a program that reads a wordlist and finds all the rotate pairs."). Only the word_list needs to be provided as argument, and a list containing lists with all rotate pairs is returned. Each word is thus contained only once in the returned list of lists.

Since the suggested approach does not need to check for the presence of a word in the list of words, the words can be provided simply as a list instead of a dict.