[NFC] Add missing revision number in libc++ ABI changelog

llvm-svn: 358411
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 5e165fba3acdb15bc7bb8ef8d44a2182ddda5e71
1 file changed