Fix "Identical code" issue in src/convert/csv-to-hdf5.js

[dasantonym]

Identical code found in 1 other location (mass = 109)

https://codeclimate.com/github/Chamberlab/node-chamberbrain-lab-kit/src/convert/csv-to-hdf5.js#issue_599b11afe6b95d0001000040