[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at cea0599 [LangRef] Adds llvm.loop.mustprogress loop metadata
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   cea0599..ab7ef35  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to ab7ef35d3460762165be8b22eb2a07a808f8f828.
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!