[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at ec489ae [IPSCCP] Fix a bug that the "returned" attribute is not cleared when function is optimized to return undef
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   ec489ae..f80866b  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to f80866bd4a2a4e8b650aef1f9a88870dd336e20f.
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!