[Clas12_calcom] [EXTERNAL] RICH time calibration

[Marco Mirazita]

Dear Timothy,
I have updated the RICH time walk correction constants for RGA spring 
2018 data set, see the logbook entry 
https://logbooks.jlab.org/entry/4321261.
These constants have been calculated from all the runs I calibrated so 
far and I don't expect to have to change them in the final calibration.
Best regards,
Marco