Update firstConsumer.rst

Replaced obsolete "x.UseRabbitMqRouting();" with "x.UseRabbitMq();" call.  Also cleaned up unit test instructions to make it more explicit that only the "...RabbitMQ" package needs to be installed and that VS12/13 people might want a different package if they're unfamiliar with NUnit.
Merge pull request #220 from jlampeatgithub/patch-1

Update firstConsumer.rst