Avoid SciPy deprecation warning.

[moorepants]

=========================================== warnings summary ============================================
cyipopt/scipy_interface.py:29
  /home/moorepants/src/cyipopt/cyipopt/scipy_interface.py:29: DeprecationWarning: Please use `MemoizeJac` from the `scipy.optimize` namespace, the `scipy.optimize.optimize` namespace is deprecated.
    from scipy.optimize.optimize import MemoizeJac

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

[nrontsis]

This PR did not solve the issue. MemoizeJac is not exported to scipy.optimize, and as far as I understand it's not part of the public API of scipy anymore.

If we want to avoid the warning with minimal changes we can do:

~~from scipy.optimize._optimize import MemoizeJac~~

[moorepants]

I'd rather not import from a private module. You can disable the warning in your code if you don't want to see it.

We'll have to find an alternative eventually. I've opened #160.