yaml_tree.rb: fix anchor
\Z
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49307 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
yaml_tree.rb: fix anchor
anchors like
\Z
are not valid inside character class. usenegative-lookahead instead.
Fixes: https://github.com/tenderlove/psych/issues/221
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49307 b2dd03c8-39d4-4d8f-98ff-823fe69b080e