Add missing back ticks for channel specs doc

Author: benoittgt

features/channel_specs/channel_spec.feature

@@ -4,11 +4,11 @@ Feature: channel spec
   Channel specs are marked by `:type => :channel` or if you have set
   `config.infer_spec_type_from_file_location!` by placing them in `spec/channels`.
 
-  A channel spec is a thin wrapper for an ActionCable::Channel::TestCase, and includes all
+  A channel spec is a thin wrapper for an `ActionCable::Channel::TestCase`, and includes all
   of the behavior and assertions that it provides, in addition to RSpec's own
   behavior and expectations.
 
-  It also includes helpers from ActionCable::Connection::TestCase to make it possible to
+  It also includes helpers from `ActionCable::Connection::TestCase` to make it possible to
   test connection behavior.
 
   Background: