doc: json support with node@12.7 esm modules

[amitport]

in node 12.7 documentation you have in
https://nodejs.org/docs/v12.7.0/api/esm.html#esm_code_import_code_statements
"JSON and Native modules are not supported"

but then go on in https://nodejs.org/docs/v12.7.0/api/esm.html#esm_json_modules and describe JSON support (which works fine)

[Trott]

Fixed in 8a10b50. Docs should be updated with the next release. Thanks!