Rename figure 3.04

Author: hollasch

books/RayTracingTheRestOfYourLife.html

@@ -304,7 +304,7 @@
 between 0 and 2 whose probability is proportional to itself: $r$. We would expect the PDF $p(r)$ to
 look something like the figure below, but how high should it be?
 
-  ![Figure [linear-pdf]: A linear PDF](../images/fig.linear-pdf.jpg)
+  ![Figure [linear-pdf]: A linear PDF](../images/fig-3.04-linear-pdf.jpg)
 
 <div class='together'>
 The height is just $p(2)$. What should that be? We could reasonably make it anything by