Fix wrong row order in the plot.model_performance

[maksymiuks]

Closes #49

[pbiecek]

@maksymiuks Thank you very much would you add a short description of this behavior to the function documentation (one line is more than enough)

[maksymiuks]

Sorry, it slipped through my radar.

@pbiecek I think we should release the package to CRAN after merging this new one. The Current version is over 1.5 years old and is missing some features.