[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 80a0dc5 [X86][AVX] computeKnownBitsForTargetNode - add VTRUNC/VTRUNCS/VTRUNCUS known zero upper elements handling.
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   80a0dc5..92bcd24  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 92bcd240f2565a79f94e0e9ac926b9135f03cbd6.
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!