Fix x-axis label for figure 3.08 (#1618)

Resolves #1532

Author: hollasch

CHANGELOG.md

@@ -24,6 +24,7 @@ Change Log / Ray Tracing in One Weekend
 ### The Rest of Your Life
   - Fix    -- Fix typo of "arbitrary" (#1589)
   - New    -- Added a bit more explanation of Buffon's needle problem (#1529)
+  - Fix    -- Fix X-axis label for figure 3.08 (Approximating the nonuniform f()) (#1532)
   - Fix    -- Corrected scatter angle theta range in section 3.5.3 (The Scattering PDF) (#1331)
   - Fix    -- Clarify the distinction between average and expected value (#1535)