Fix Y-axis start point for graph cells

Closes #54 

Removes whitespace under the graph column by adjusting the starting point by one unit.

iPad Retina:
![image](https://cloud.githubusercontent.com/assets/235010/4338619/1dddac44-401b-11e4-8fc8-342975d6b977.png)

iPad 2:
![image](https://cloud.githubusercontent.com/assets/235010/4338629/3649c1e6-401b-11e4-9731-5039839b0fb3.png)

iPhone 5:
![image](https://cloud.githubusercontent.com/assets/235010/4338637/46447c62-401b-11e4-927c-67525145903b.png)