Gem Dependency Errors

[JustinTBrown]

I've included gem "middleman-sync", "~> 3.0.12" in config.rb but when attempting to bundle install I receive the following error:

Bundler could not find compatible versions for gem "builder":
  In Gemfile:
    middleman-sync (~> 3.0.12) ruby depends on
      builder (~> 2.1.2) ruby

    builder (3.2.2)

It's telling me that I require Builder 2.1.2 or above, but I actually have Builder 3.2.2. Anyone know what the problem is?