Occasional skopt.utils.expected_minimum error

[taalbrecht]

Scipy has an underlying bug in scipy.optimize.minimize when evaluating points on the border of a design space. If the point is exactly on the border, scipy will attempt to evaluate points outside of the design space to estimate the gradient. This causes an error per the following issue documented here:

scipy/scipy#3056 (comment)

This issue has been fixed in scipy 1.5.0:

scipy/scipy#10673

Recommend updating setup.py to require scipy >= 1.5.0 to fix this issue.