Fix dictionary completion on Pandas objects.
Fix dictionary completion on Pandas objects.

This should fix the following error:

  File ".../ptpython/completer.py", line 373, in _get_expression_completions
    elif result:
  File ".../pandas/core/generic.py", line 1330, in __nonzero__
    f"The truth value of a {type(self).__name__} is ambiguous. "

jonathanslenders/ptpython