Ruby's standard JSON gem (which comes bundled with the core Ruby distribution!).
ruby-json contains code that is not Free under the FSF's definition, not Open Source under the OSI's definition, and not GPL-compatible. This has caused much consternation among folks who care about any of those 3 things.
This PR replaces that non-Free code with Free code, removing friction for Ruby users on GNU/Linux distros that care about those 3 things.