[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 5a50f8b [AArch64][GlobalISel] Add legalization and selection support for <4 x s16> G_SHL.
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   5a50f8b..721d57f  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 721d57f952ba0dbe02908fc897374dd6324668b9.
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!