Depend on Bunny ~> 2.9.0

Which in turn will depend on amp-protocol 2.3.x. Earlier Bunny versions won't work
with that amp-protocol release series.

See ruby-amqp/bunny#538 and Bunny change log for details.

Author: michaelklishin

sneakers.gemspec

@@ -19,7 +19,7 @@ Gem::Specification.new do |gem|
   gem.test_files    = gem.files.grep(/^(test|spec|features)\//)
   gem.require_paths = ['lib']
   gem.add_dependency 'serverengine', '~> 2.0.5'
-  gem.add_dependency 'bunny', '~> 2.7.2'
+  gem.add_dependency 'bunny', '~> 2.9.0'
   gem.add_dependency 'concurrent-ruby', '~> 1.0'
   gem.add_dependency 'thor'