fixed bug following from introduction of parse_fakepdf in config.py
Created by: comane
Because of the introduction of the parse_fakepdf method in config.py, the val corresponding to the "fakepdf" key of the datacuts dict in produce_fitunderlyinglaw function is not type str anymore but core.PDF. This leads to an error when running vp-comparefits:
[ERROR]: Bad configuration encountered: Bad input type for parameter 'pdf': Value 'NNPDF40_nnlo_as_01180' is not of type str, but of type 'PDF'.