Replace deprecated np.int with int in bench_ml.py and transformers.py

[hardefarogonondo]

This pull request addresses the use of the deprecated np.int in the bench_ml.py and transformers.py files.

This change helps maintain compatibility with future versions of Python and NumPy and avoids potential deprecation errors.

Specifically, the changes include:

• In benchmark/bench_ml.py, all instances of np.int were replaced with int.
• In skopt/space/transformers.py, all instances of np.int were replaced with int.

All tests have passed after these modifications. This change does not affect any functionalities or performance.

[hardefarogonondo]

Hello,

While my pull request triggered a CircleCI build, the build failed due to an issue that doesn't appear to be related to my changes. The error message suggests that CircleCI is unable to access the Debian "Stretch" repositories because they no longer have a Release file:

Reading package lists...
E: The repository 'http://security.debian.org/debian-security stretch/updates Release' does no longer have a Release file.
E: The repository 'http://deb.debian.org/debian stretch Release' does no longer have a Release file.
E: The repository 'http://deb.debian.org/debian stretch-updates Release' does no longer have a Release file.

Exited with code exit status 100
CircleCI received exit code 100

Could you please look into this? It seems to be a problem with the CircleCI configuration, not with the changes in this pull request.

Thank you.