QPID-5794: Fix the regex in spout.rb

In Ruby > 1.8 the regular expression worked as is. But in 1.8 it
requires that the braces be escaped.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1598629 13f79535-47bb-0310-9956-ffa450edef68