Preserve timezone when calling to_time

Quoting the Rails DateAndTime::Compatibility module:

> With Ruby 2.4+ the default for +to_time+ changed from
> converting to the local system time, to preserving the offset
> of the receiver. For backwards compatibility we're overriding
> this behavior

We don't need backwards compatibility in our application because we
aren't converting any time objects to the local system timezone but use
the application timezone all the time instead.

config/application.rb

@@ -11,7 +11,6 @@ module Consul
     config.load_defaults 5.0
 
     # Overwrite Rails 5.0 defaults and use the options we used in Rails 4
-    ActiveSupport.to_time_preserves_timezone = false
     config.active_record.belongs_to_required_by_default = false
     config.ssl_options = {}