[www-scripts] Clang Attribute Doc Update: ERROR

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UPDATING LLVM SOURCES
HEAD is now at 9267cae [ELF] Don't error on R_PPC64_REL24/R_PPC64_REL24_NOTOC referencing __tls_get_addr for missing R_PPC64_TLSGD/R_PPC64_TLSLD
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   9267cae..05bef88  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 05bef88eb3ecb8519a871ca9aa53caeca5add555.
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!