Upgrade sphinx-autodoc-typehints to 1.2.0

[fabaff]

1.2.0

• Fixed compatibility with Python 3.6 and 3.5.3
• Fixed NameError when processing signatures of wrapped functions with type hints
• Fixed handling of slotted classes with no __init__() method
• Fixed Sphinx warning about parallel reads
• Fixed return type being added to class docstring from its __init__() method
  (thanks to Manuel Krebber for the patch)
• Fixed return type hints of @property methods being omitted (thanks to pknight for the patch)
• Added a test suite (thanks Manuel Krebber)

[mention-bot]

@fabaff, thanks for your PR! By analyzing the history of the files in this pull request, we identified @bbangert to be a potential reviewer.