.rvmrc switched to .ruby-* files to comply with RVM suggestions

RVM is deprecating the .rvmrc configuration file, because it needs user authorization to run the bash script inside of it.

I saw that your .rvmrc file only contains the reference to the ruby version and gemset to be created automatically by RVM,  and it doesn't have any additional bash script. In this case, RVM suggest to create .ruby-version and .ruby-gemset files, which contains the version of Ruby and the name of gemset, respectively.