bistro/bistro/server/HTTPMonitor.cpp: fix shadow error
bistro/bistro/server/HTTPMonitor.cpp: fix shadow error

Summary:
Fix errors exposed by gcc's -Wshadow-compatible-local.
See https://fburl.com/bad-shadow for justification.
I'm now removing the exemptions. See T25277067.

Rename inner "d" to "dObj".

This avoids the following errors:

  bistro/bistro/server/HTTPMonitor.cpp:105:13: error: declaration of 'folly::dynamic d' shadows a parameter [-Werror=shadow-compatible-local]

Reviewed By: yfeldblum

Differential Revision: D6771718

fbshipit-source-id: dfdc5ee9b2cd106ab8dc2209c92b339d3f8badd3

facebook/bistro,facebook/bistro,facebook/bistro,facebook/bistro,facebook/bistro,facebook/bistro