Update calculate_R_Zh_relationship (#72)
Update calculate_R_Zh_relationship (#72)

Updated this to fix an issue where the field "rain_rate" was not called as a field in only one spot of the calculation of R(Z) relationship.
nguy/PyDisdrometer,nguy/PyDisdrometer,josephhardinee/PyDSD,josephhardinee/PyDisdrometer,josephhardinee/PyDSD,josephhardinee/PyDisdrometer