* doc/syntax/literals.rdoc: [DOC] Single quote strings allows escape
  of backslash as well, patch by @idupree [Fixes GH-553] [ci skip]
  https://github.com/ruby/ruby/pull/553


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45332 b2dd03c8-39d4-4d8f-98ff-823fe69b080e