NO-JIRA: Fixed Ruby "uninitialized constant Date (NameError)" error

The gem now requires the "date" feature be available.

It doesn't show up when running the Rspec tests, but showed up when
running an example app.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1491783 13f79535-47bb-0310-9956-ffa450edef68