Gem install issues with Ruby 1.9.2

[jgamedev]

On my system running Ubuntu 15.04, when trying to use Ruby 1.9.2 as a local version (using rbenv as a version manager), I get a few gem installation errors similar to this one:

Gem::InstallError: execjs requires Ruby version >= 1.9.3.

Using latest 1.9.3 release instead of 1.9.2 which is suggested in the readme file fixes it for me. Please consider updating the installation instructions, if that's the case.

(Disclaimer: I might have deleted the gemlock file prior to running bundle install, maybe this is the cause)