Temporarily pin HyperSpy to version < 2.0 for kikuchipy v0.9

[hakonanes]

Description of the change

We pin HyperSpy to version < 2. This is a temporary solution for the imminent kikuchipy v0.9.

See #650 for the progress on support for HyperSpy 2.0.

Progress of the PR

• [n/a] Docstrings for all functions
• [n/a] Unit tests with pytest for all lines
• Clean code style by running black via pre-commit

For reviewers

• The PR title is short, concise, and will make sense 1 year later.
• New functions are imported in corresponding __init__.py.
• New features, API changes, and deprecations are mentioned in the unreleased
  section in CHANGELOG.rst.
• New contributors are added to release.py, .zenodo.json and
  .all-contributorsrc with the table regenerated.