Change method call

On 1891af32, I changed the name of Synplot method that saves the
spectrum. At that time, I did not change the call for this method on the
tests and example.
Change chi-square plot for 2 variables

The plot showing the distribution of chi-square for two variable was
presented using color scale. But it was very difficult to infer anything
from it. Thus, I decided to change it to a contour plot.
Run example to update plots

I changed the chi-square distribution plot for two parameters. I run the
notebook to update those plots.