Bump March Hare to 3.0+
Bump March Hare to 3.0+

Despite the major version bump, there are effectively
no user-facing changes:
https://github.com/ruby-amqp/march_hare/blob/master/ChangeLog.md#changes-between-2220-and-300-february-20th-2017.

gocardless/hutch,Fatsoma/hutch,gocardless/hutch,Fatsoma/hutch,Fatsoma/hutch,gocardless/hutch