[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at e1644a3 GlobalISel: Reduce G_SHL width if source is extension
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   e1644a3..512e256c master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 512e256c0d8c0fed5b4603ed5ed74b6ad503f368.
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!