function use(plugin) {
  if (plugins.indexOf(plugin) === -1) {
    plugins.push(plugin);
    plugin(core);
  }
}
Utility function for registering plugins.

Plugins are simple functions that are passed the core jscodeshift instance.
They should extend jscodeshift by calling `registerMethods`, etc.
This method guards against repeated registrations (the plugin callback will only be called once).

@augments core
@static
@param {Function} plugin