[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at ba447f3 [NFC][lldb] Silence unused variable warning
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   ba447f3..1f852ba  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 1f852ba8534cc773c114165e77acba411ac25a93.
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!