change the error message in runner

In line 155 in runner.py we can't rely on __name__ because a functools.partial object has no attribute __name__.

~/Work/induced_gap_B_field/adaptive/runner.py in _run()
    353                     except Exception as e:
    354                         raise RuntimeError(
--> 355                             'An error occured while evaluating '
    356                             f'"{self.learner.function.__name__}({x})". '
    357                             'See the top traceback for details.'

AttributeError: 'functools.partial' object has no attribute '__name__'

@jbweston