[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 8671166 [clang-tidy] Fix bugprone-bad-signal-to-kill-thread crash when `SIGTERM` was undefined after definition.
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   8671166..4357986  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 4357986b411dd164932c66ebfe4a9cf96a7d74cd.
CMake Error at CMakeLists.txt:3 (cmake_minimum_required):
  CMake 3.13.4 or higher is required.  You are running version 3.7.1


-- Configuring incomplete, errors occurred!