inconsistency in argon channels

[mcolomermolla]

Both channels_argon_he.dat and channels_argon.dat point to *_he channels

Note:
Therefore, if one runs:
rc.run(flux, detector='ar40kt', material='argon'), it doesn't finds the efficiency files where they should be

[JostMigenda]

Indeed, that looks like a simple copy & paste error in channels_argon.dat. Thanks for spotting it!
Do you want to submit a PR with the fix or should I?