[www-scripts] Clang Attribute Doc Update: ERROR

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UPDATING LLVM SOURCES
HEAD is now at 6ef0711 [scudo/standalone] Fix leak in ThreadedGlobalQuarantine test
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   6ef0711..325d95e  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 325d95e72d99a8fe12ff3514f9dbf957681f436b.
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!