Wrong figure reference (4.2 instead of 4.3) on p. 54

[danm0nster]

In the first line of the subsection titled "Comparisons, visual and numerical" there is a reference to Figure 4.2, which should be to Figure 4.3.

[avehtari]

Thanks! This was previously reported in #20 and is also listed in the errata https://avehtari.github.io/ROS-Examples/errata.html