Import kfold.stanreg instead of kfold

[jgabry]

This is just a heads up about something that will need to be fixed once the next versions of loo and rstanarm are released. In the upcoming release of version 2.1.0 of the loo package we will be exporting a generic kfold function and the next rstanarm will import that generic and then provide a kfold.stanreg method. This will result in a warning when checking the psycho package because you are currently importing all of the loo package and also importing kfold from rstanarm. Once loo and rstanarm are released you can easily fix the problem by importing just kfold.stanreg from rstanarm instead of kfold. If you have any trouble let me know and I can help out.