Session04 - trigrams.py finished

I'm going to agree with @jefrailey on this one.  You want to use the modulus operator (`%`)rather than division to get this answer.  Because of the nature of floats and how they are stored in memory, you cannot count on the actual value of a float being the same as what you see represented.  For more information, [read this essay from the Python docs](https://docs.python.org/2/tutorial/floatingpoint.html)