Add and appy RSpec/Rails/TravelAround rubocop rule

This rule was added in rubocop-rspec 2.19.0.

When freezing time in a test, `travel_back` is called automatically when
the test finishes, so we can do it in a `before` block instead of an
`around` block.

Note this rule didn't detect our usage of `freeze_time` because we were
using it on cops with a certain tag, but I expect the rule to be able to
detect this usage in the future.

.rubocop.yml

@@ -561,6 +561,9 @@ RSpec/Rails/HaveHttpStatus:
 RSpec/Rails/InferredSpecType:
   Enabled: true
 
+RSpec/Rails/TravelAround:
+  Enabled: true
+
 RSpec/RepeatedExample:
   Enabled: true
 

spec/spec_helper.rb

@@ -148,9 +148,7 @@ RSpec.configure do |config|
       .to receive(:locales).and_return(I18n.available_locales.map(&:to_s))
   end
 
-  config.around(:each, :with_frozen_time) do |example|
-    freeze_time { example.run }
-  end
+  config.before(:each, :with_frozen_time) { freeze_time }
 
   config.before(:each, :application_zone_west_of_system_zone) do
     application_zone = ActiveSupport::TimeZone.new("Quito")