Bundler could not find compatible versions for gem "thor":
  In snapshot (Gemfile.lock):
    thor (>= 1.1.0)

  In Gemfile:
    font-awesome-rails was resolved to 4.7.0.7, which depends on
      railties (>= 3.2, < 7) was resolved to 6.1.4, which depends on
        thor (~> 1.0)

    retscli was resolved to 0.2.0, which depends on
      thor (~> 0.19)

Running `bundle update` will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.