Rails 3.1 now uses uglifier by default, which depends on multi_json 1.0.3. This gem is currently specified with multi_json ~> 0.0.5, so this results in a compatibility problem when using this gem in an rails app.
Bumping multi_json to 1.0.3 solves this, tests pass, and I haven't been able to find anything wrong in manual testing as a result of the change.
Bump multi_json version to allow compatibility with uglifier in rails 3
I'm using omniauth in my project and it also depends on multi_json 1.0.3