scikit-image 0.18.3

This is a small bugfix release for compatibility with Pooch 1.5 and SciPy 1.7.

Bug fixes

• Only import from Pooch's public API. This resolves an import failure with
  Pooch 1.5.0. (#5531, backport of #5529)
• Do not use deprecated scipy.linalg.pinv2 in random_walker when
  using the multigrid solver. (#5531, backport of #5437)