ChangeLog: fix a typo. [ruby-core:66328] [Backport #10521]
           https://github.com/ruby/ruby/pull/760


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@48610 b2dd03c8-39d4-4d8f-98ff-823fe69b080e