message: Fix GYP build break due to directory change of jsoncpp.
  This CL updates our GYP file to refer to the new directory.
diff: 'target_name': 'jsoncpp',
  'type': 'static_library',
  'variables': {
  - 'jsoncpp_root': '<(third_party_dir)/jsoncpp',
  + 'jsoncpp_root': '<(third_party_dir)/jsoncpp/v1_7_6',
  'jsoncpp_srcs': [
  '<(jsoncpp_root)/src/lib_json/json_reader.cpp',
  '<(jsoncpp_root)/src/lib_json/json_value.cpp',
  