Add missing Errno::ECONNREFUSED to HTTP_ERRORS(#1089)
Add missing Errno::ECONNREFUSED to HTTP_ERRORS(#1089)

Adds `Errno::ECONNREFUSED` to the list of `HTTP_ERRORS` to improve
error handling, so that we can do the following in applications
generated by Suspenders:

```ruby
begin
  some_http_call
rescue *HTTP_ERRORS => error
  # Handle error
end
```
thoughtbot/suspenders,thoughtbot/suspenders,thoughtbot/suspenders