[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at ec54867df [SCEV] Model `ashr exact x, C` as `(abs(x) EXACT/u (1<<C)) * signum(x)`
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   ec54867df..b77dd32 master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to b77dd32a6fcc53908aaffc065d4d5b05026ddda7.
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!