Replaced echo for printf when using formatted strings

Updated version list (see screenshot), installed versions in blue (as it was before), current version in green with an arrow (`->`) in front of it.

Before the `nvm ls` command didn't show colors due to the difference in multiline string handling in zsh. This is now also fixed.

![screen shot 2014-03-17 at 13 21 46](https://f.cloud.github.com/assets/351038/2435754/c133098c-adce-11e3-8276-423a4fac4e3b.png)