[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 1d9b860 Unify the return value of GetByteSize to an llvm::Optional<uint64_t> (NFC-ish)
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   1d9b860..6a75496  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 6a75496836ea14bcfd2f4b59d35a1cad4ac58cee.
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!