[ruby/open-uri] Add documentation for request_specific_fields option
request_specific_fields
https://github.com/ruby/open-uri/commit/2e7734c061
[ruby/open-uri] Add documentation for
request_specific_fieldsoptionhttps://github.com/ruby/open-uri/commit/2e7734c061