Fix ruby-build errors with ruby 2.1.1

Apply mislav's
[patch](https://github.com/sstephenson/ruby-build/issues/526#issuecomment-37933242)
against a readline bug in newer rubies. Should fix #219 and #218, and
we'll remove when a new ruby is released or if ruby-build patches
this bug itself.
Remove support for EOL'd ubuntus: 12.10 and 13.04