[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 7e2ffe7 [llvm-exegesis] Do not silently fail on unknown instruction encoding formats.
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   7e2ffe7..419168d  master     -> origin/master
Auto packing the repository for optimum performance. You may also
run "git gc" manually. See "git help gc" for more information.
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 419168d9381959ec6850e9e87aff9d062b68ef4b.
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!