[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at ff1002a [Attributor][NFC][AAPotentialValues] Change interface of PotentialValuesState
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   ff1002a..4b211b9  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 4b211b94d71386d249e2004c817a9bb659634c2b.
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!