src: fix compiler warning from SetAccessor

Currently the following compiler warning is displayed when building:

../src/node.cc:3270:12: warning: 'SetAccessor' is deprecated
[-Wdeprecated-declarations]
  process->SetAccessor(FIXED_ONE_BYTE_STRING(env->isolate(), "ppid"),
           ^
../deps/v8/include/v8.h:3184:22: note: 'SetAccessor' has been
explicitly marked deprecated here
                bool SetAccessor(Local<Name> name,

This commit updates the call to use the Maybe version.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

src