Rails example is not threadsafe

[kingdonb]

https://github.com/3scale/3scale_ws_api_for_ruby#a-rails-example

The example provided in Rails Example section of the README is not thread-safe. This is not a good example because the default Rails web server today, puma, is threaded.

A better example might include this method for create_client instead:

def create_client
  @@threescale_client ||= {}
  @@threescale_client[Thread.current.name] ||=
    ThreeScale::Client.new(service_tokens: true)
end

I am not an expert but when I was hitting my API several times within the space of a second, I was getting some calls out to 3scale aborted with a response from "openresty" that looked like a header was placed into the body by accident.

It seems to me this could only be a threading issue, because it went away when I gave each worker thread his own 3scale client.

> puts body
HTTP/1.1 200 OK
Server: openresty
Date: Thu, 15 Nov 2018 14:45:56 GMT
Content-Type: application/vnd.3scale-v2.0+xml
Con

intercepted at lib/3scale/client.rb ~ line 368 instead of the expected response body:

<?xml version="1.0" encoding="UTF-8"?><status><authorized>true</authorized><plan>Your Plan Name Here</plan></status>