setting version for json dependency at '~> 1.8'

I hope I can quick fix this stupid problem:

Bundler could not find compatible versions for gem "json":
  In snapshot (Gemfile.lock):
    json (1.8.0)

  In Gemfile:
    ruby-trello (>= 0) ruby depends on
      json (>= 0) ruby

Running `bundle update` will rebuild your snapshot from scratch, using only the gems in your Gemfile, which may resolve the conflict.

no, it doesn't :-(