[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at b3afad0 [GlobalISel] Add a `X, Y = G_UNMERGE(G_ZEXT Z)` -> X = G_ZEXT Z; Y = 0 combine
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   b3afad0..2c12b05  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 2c12b056bececd3fce3d5a3b731b4ff8fa6dfbbb.
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!