[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at af1c1e2 AMDGPU/GlobalISel: Implement computeKnownBits for groupstaticsize
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   af1c1e2..7f717b6  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 7f717b6d1f65f8474e8633b040a16c55f0ad6b96.
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!