update rvm
rvm get stable
list rubies
rvm list known
install ruby 2.4
rvm install 2.4
new application
rvm gemset create newapp
rvm gemset use newapp
gem install rails --version 4.2.6
gem install rails --pre # last one
rails new newapp -T -d postgresql --skip-bundle
cd newapp
rvm --ruby-version use 2.2.0@newapp --create
edit Gemfile
bundle
Configurar database.yml
rake db:create