fix cattle_cycles

Author: HumphreyYang

lectures/cattle_cycles.md

@@ -270,6 +270,7 @@ c2 = np.array([[0, 0,  0],
                [0, 1,  0],
                [0, 0, 15]])
 
+πh = πh.item()
 ub = np.array([[πh * a0, 0, 0, πh]])
 uh = np.array([[50, 1, 0, 0]])
 um = np.array([[100, 0, 1, 0]])