[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 9237e73 [Hexagon] Replace HexagonISD::VSPLAT with ISD::SPLAT_VECTOR
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   9237e73..3758495  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 375849518db97096212f7f2b996b0d15f97be959.
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!