Superfluous apostrophe removed

It should say: send messages to its subscribers, not subscriber's
Fix docs to show interactions, not method calls

The code listing is supposed to show interactions, but a missing "1 * " made them method calls
Superfluous apostrophe removed again

It should say hellos, not hello's
Merge pull request #43 from magdzikk/groovy-1.8

Fix incorrect code listing in docs