[ruby/psych] Fixing compatibility with libyaml 0.2.5

The main issue is that commas aren't allowed in local tags.  libyaml
was updated to follow the spec, and our tests were out of date.

See: https://github.com/yaml/libyaml/issues/196

https://github.com/ruby/psych/commit/3f5e520fd3

Note that this is not security fix, but need for release processs.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@67885 b2dd03c8-39d4-4d8f-98ff-823fe69b080e