Change Cauchy draws seed so figure matches prose

The prose says "a few sudden large deviations from the mean" but
seed 11 produced only one large deviation. Seed 10 gives three
clearly visible deviations (45, -49, -62), all within the y-axis
range of (-120, 120).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jstac

lectures/heavy_tails.md

@@ -349,7 +349,7 @@ mystnb:
     name: draws-normal-cauchy
 ---
 n = 120
-rng = np.random.default_rng(11)
+rng = np.random.default_rng(10)
 
 fig, axes = plt.subplots(3, 1, figsize=(6, 12))