Rake task to update subscriber list tags

When a topic changes, we should update the Subscribers List in Email
Alert API to keep subscribers updated.
This should be done by creating a new entry for the updated topic with
the same govdelivery identifier.

https://www.pivotaltracker.com/story/show/83840958
This looks like it has code injection vulnerabilities: ie, what if "key" has something like the string '=>' as part of it?