Fix number of shares so minimize can be solved

With 1000 shares, the solution does not exist. n_shares = 15 matches the
article.

Author: bryanwweber

python-scipy-cluster-optimize/minimize_constrained.py

@@ -2,7 +2,7 @@
 from scipy.optimize import minimize, LinearConstraint
 
 n_buyers = 10
-n_shares = 1000
+n_shares = 15
 np.random.seed(10)
 prices = np.random.random(n_buyers)
 money_available = np.random.randint(1, 4, n_buyers)