Fix for IOB calculations not using pumphistory-merged.json

Per #554, oref0 0.5.1 was improperly using pumphistory-zoned.json for IOB calculations instead of pumphistory-merged.json, which resulted in IOB for any given bolus or temp basal event being cut off after 2 hours. As a result, oref0 would have been slightly less likely to low-temp when BG was running low 2-3 hours after a meal, and would stop issuing SMBs after 2 hours if it calculated there was no more COB.

This release fixes that issue by correcting the iob.json report to use pumphistory-merged.json as intended.