I made my own chart, but I'll actually tell you where the numbers came from. I used the average gas price from the last year as a starting point and then applied a modest 4% increase per year - even though it has been more than double that for almost the last 10 years.
I also discarded their number for the PiP because it makes no sense and instead used the value from the regular Prius * 0.75 + the value from the Leaf * 0.25
Here is my chart:
Then I made another chart and assumed that gas was going to increase at 7% for the next 12 years - which is still less than it has for the last 10.
It must be true, there is a chart!