Ensure plots with Year on X-Axis have only integers

[pancakereport]

Closes #165

I understand if we don't want to merge this because it definitely goes beyond the simplicity in Data 8.

From what I looked into, Year is already definitely full of integers. When I cast it to integers, the plot doesn't change at all. What's happening is a result of how matplotlib decides to show the plot. We can edit the datascience package if you'd like (something like "if x or y values are integers, then insert my fix here). Or we can just leave it as is.