ruby-install needs to be at v0.4.3 in order to install Ruby 2.1.2.

I have no idea how 9ca8d9afdc3f6a06dcefda330e3731e79675d9d7 ever worked... or if it did. But according to the [ruby-install Changelog](https://github.com/postmodern/ruby-install/blob/master/ChangeLog.md) you need at least v0.4.3 of ruby-install to get Ruby 2.1.2

/cc @atomic-penguin