DOC: change example sample spacing

Change the sample spacing in the example so the linear interpolation points line up with the original points

![original](https://cloud.githubusercontent.com/assets/58611/5332958/6e65ac3a-7e36-11e4-9499-4a41b508aaed.png)

![new](https://cloud.githubusercontent.com/assets/58611/5331722/3b60835e-7e05-11e4-989d-9f6517401bac.png)