Update of LYRA level2

The calibration of LYRA data (level 2) has been updated on December 31 2016 00:00:00 to take into account new information about the evolution of dark current, as well as the result of the last calibration campaigns. This update currently results in a small amplitude jump in the timeseries. This jump should disappear the next time the data will be reprocessed, in a few months.