[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 12bdd42 [APFloat] Improve asserts in isSignificandAllOnes and isSignificandAllZeros so they protect shift operations from undefined behavior.
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   12bdd42..2c9dc7b  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 2c9dc7bbbf514b1ed7bdefacb3213beae5916b3d.
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!