[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 721d57f [X86] Return from SimplifyDemandedBitsForTargetNode after calculating known bits for VSHLI/VSRAI/VSRLI.
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   721d57f..f64903f  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to f64903fd81764f1fde7aeb00eea5e1d488458f63.
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!