[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at c0958b7 [mlir] Add support for referencing a SymbolRefAttr in a SideEffectInstance
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   c0958b7..6b0fc1f  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 6b0fc1f3c161295e6577d4c2237cefcb8e4dd9ba.
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!