Change dimension of mapping histogram. Mapping histogram currently ignores bins with zero entries, whcih is a probelm for MINERvA CC0pi antinu. This leads to the data histogram having 60 bins and the cov having 58 bins (due to the zero bins being masked out in the chi2 claculation). I think this solves it, but am a little afraid of committing to large changes in the mapping and want to check it further