[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at a1de391 [LV][NFC-ish] Allow vector widths over 256 elements
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   a1de391..1e2da38  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 1e2da3839cc3543629ecb847fd3aa34edb64b42a.
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!