[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 137da82 [mlir][CAPI] Remove the exclusion of the MLIR C-API from libMLIR.so.
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   137da82..8a5858c  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 8a5858c8fd50e6f5767a21854951c3ccba17e8c4.
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!