doc: correct argument names
doc: correct argument names

The function signatures use "json", not "root".

npmccallum/jansson,akheron/jansson,markalanj/jansson,AmesianX/jansson,wirebirdlabs/featherweight-jansson,akheron/jansson,AmesianX/jansson,bstarynk/jansson,wirebirdlabs/featherweight-jansson,akheron/jansson,markalanj/jansson,Mephistophiles/jansson,bstarynk/jansson,markalanj/jansson,Mephistophiles/jansson,npmccallum/jansson,bstarynk/jansson