[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at ddb4693 [libcxx] [test] Add (void) return casts on functions marked nodiscard in MS STL
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   ddb4693..0a7cd99  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 0a7cd99a702595ccf73c957be0127af9f25fb9a2.
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!