change "sklearn" to "scikit-learn" in INSTALL_REQUIRES

[simon-schmitz]

Hello,

I encountered a problem when installing pykep with Python3.8. This is likely due to the fact that in "tools/wheel_setup.py" the INSTALL_REQUIRES has the entry "sklearn". However, according to the error message below this is deprecated and should be replaced by "scikit-learn". Could you please take care of this?

Thanks a lot in advance!
Simon

Collecting sklearn (from pykep->my-analysis==1.0)
Downloading sklearn-0.0.post7.tar.gz (3.6 kB)
Preparing metadata (setup.py): started
Preparing metadata (setup.py): finished with status 'error'
error: subprocess-exited-with-error

× python setup.py egg_info did not run successfully.
│ exit code: 1
╰─> [18 lines of output]
The 'sklearn' PyPI package is deprecated, use 'scikit-learn'
rather than 'sklearn' for pip commands.

  Here is how to fix this error in the main use cases:
  - use 'pip install scikit-learn' rather than 'pip install sklearn'
  - replace 'sklearn' by 'scikit-learn' in your pip requirements files
    (requirements.txt, setup.py, setup.cfg, Pipfile, etc ...)
  - if the 'sklearn' package is used by one of your dependencies,
    it would be great if you take some time to track which package uses
    'sklearn' instead of 'scikit-learn' and report it to their issue tracker
  - as a last resort, set the environment variable
    SKLEARN_ALLOW_DEPRECATED_SKLEARN_PACKAGE_INSTALL=True to avoid this error
  
  More information is available at
  https://github.com/scikit-learn/sklearn-pypi-package
  
  If the previous advice does not cover your use case, feel free to report it at
  https://github.com/scikit-learn/sklearn-pypi-package/issues/new
  [end of output]

note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed
× Encountered error while generating package metadata.
╰─> See above for output.
note: This is an issue with the package mentioned above, not pip.
hint: See above for details.