This project was processing dates without proper consideration of their timezones. As such, several bizarre errors errors were happening, especially around the start and end of a sprint. For example, issues closed at 6pm Arizona time on the last day of the sprint were not having their points credited to that day on the burndown chart because GitHub returned that closed date as 1am UTC the following day. This project now processes all dates internally using UTC. The `sprint_start_date` and `sprint_end_date` are assumed to be at 00:00:00 *local time*, and the final burndown chart is rendered in local time. These changes fix #17 and fix #21