ChangeLog: fix clang version

* ChangeLog: fix clang version in r45508, 5.1 is the version by
  Apple, the upstream version is 3.4.  [ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47275 b2dd03c8-39d4-4d8f-98ff-823fe69b080e