[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at c0b3abd [MLIR] Add a foldTrait() mechanism to allow traits to define folding and test it with an Involution trait
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   c0b3abd..b49787d  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to b49787df9a535f03761c340dca7ec3ec1155133d.
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!