uninitialized constant Kraken

[Sjors]

Steps to reproduce, using RVM with Ruby 2.3.0 on a Mac (El Capitan), bundler 1.11.2:

Gemfile contents:

source 'https://rubygems.org'
ruby "2.3.0"

gem 'kraken_ruby', '0.5'

rvm install 2.3.0
gem install bundler
bundle
bundle console

In the console:

Kraken

I also tried require 'ruby-kraken', which results in LoadError: cannot load such file -- kraken-ruby

I noticed that ~/.rvm/gems/ruby-2.3.0/gems/kraken_ruby-0.5.0 is empty.

I tried without bundler as well, i.e. gem install kraken_ruby followed by irb, but no luck. I also tried with older versions of Ruby (e.g. 2.1.3) and older versions of bundler (e.g. 1.7.4).