Picongpu: travis-ci suggestions only valid for GNU sed

[PrometheusPi]

The suggestions to automatically fix malformatted printed by the travis-ci dialog are great to quickly solve formating issues - but they are only valid if une used GNU sed. They cause various issues when using BSD sed, e.g.:

• \t is only a tab in GNU, on BSD a real tab must be used (or alternatively the tr program)
• 's/[[:blank:]]\+$//' does not remove trailing whitespaces
• the flag -i requires a file extension

@ComputationalRadiationPhysics/picongpu-developers Do you think, we should additionally output equivalent commands for BSD?

[sbastrakov]

For the Windows version of GNU sed some of recommentations also do not work, while others do. Unfortunately, I do not remember which ones.

[ax3l]

I just fixed the same in WarpX for you OSX users. I will share the updates with you :)

[psychocoderHPC]

closed with #3073