Ruby 1.8.7 is not supporting octopus

[bethink]

in https://github.com/tchandy/octopus/blob/master/lib/octopus/model.rb

 def hijack_methods
    around_save :run_on_shard, :unless => -> { self.class.custom_octopus_connection }
    after_initialize :set_current_shard

-> lambda syntax supports from ruby-1.9.0.
But in rubygems.org says, octopus supports >= 0 ruby verison.

[sobrinho]

Fixed by bc77ae3