In your Gemfile, specify the version of TzInfo that suits Mongoid, before Mongoid and before rufus-scheduler (rufus-scheduler accepts any version of TzInfo).
source 'https://rubygems.org'
gem 'tzinfo', '0.3.22'
gem 'mongoid', '3.1.4'
gem 'rufus-scheduler'
UPDATE
Updated rufus-scheduler 2.0.x so that it accepts >= 0.3.22 (https://github.com/jmettraux/rufus-scheduler/commit/18c98010)
Unfortunately, can't seem to be able to push to RubyGems.org for now (it goes 500).
Until I find a workaround, you can point to that new rufus-scheduler with
gem 'rufus-scheduler', :git => 'git://github.com/jmettraux/rufus-scheduler.git', :branch => 'two'
UPDATE
Could push rufus-scheduler 2.0.24 to rubygems https://rubygems.org/gems/rufus-scheduler
It should be OK now.