src: make ReqWrap req_ member private
Checklist
-
make -j4 test
(UNIX), orvcbuild test nosign
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
src
Description of change
This commit attempts to address one of the items in https://github.com/nodejs/node/issues/4641 which is related to src/req-wrap.h and making the req_ member private.