我试图通过明亮的盒子在Ubuntu上的rails上安装ruby。我安装了：
sudo apt-get install software-properties-common
sudo apt-add-repository ppa:brightbox/ruby-ng
sudo apt-get update
sudo apt-get install ruby ruby-dev
但是当我尝试安装时：
sudo apt-get install ruby-switch
我收到此错误：
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package ruby-switch is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'ruby-switch' has no installation candidate
问题是什么，以及如何解决？