Fix typo in rummager stub and message reset

This did not fail or raise an error because:

 1. `rummager_api` is a method in the wiring
 2. The wiring is included in the entire cucumber World
 3. The tests using this were then matching original requests.
Merge pull request #258 from alphagov/fix-republishing-test-typo

Fix typo in rummager stub and message reset