[www] cxx_status: Update Reflection TS to Cologne draft

Summary:
As of the 2019 Cologne meeting, according to its minutes (N4826), N4818
is the draft of the Reflection TS.

Reviewers: rsmith, aaron.ballman

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D75524