Drop incorrect port

`Rack::Request#url` includes the port of the original request (despite
accurate scheme updates). This becomes an issue when LB terminates SSL:

- client request is made to https://example.com:443,
- LB request is http://example.com:80
- build_api_url returns correct scheme but wrong port:
  https://example:80

Since we only need the request url from the env, this changeset manually
fetches the correct scheme (Rack accounts for FWD headers already), the
host (w/out port as opposed to #host_with_port), and the fullpath
(pathname + query params)

Another benefit of this changeset is that it no longer mutates the
original env object (assigning to `new_env` is by reference).

Caveat: im dropping @options[:protocol] bc there's x-fwd-proto should
handle this already.

Author: Peleg

lib/prerender_rails.rb

@@ -181,32 +181,14 @@ def get_prerendered_page_response(env)
       end
     end
 
-
     def build_api_url(env)
-      new_env = env
-      if env["CF-VISITOR"]
-        match = /"scheme":"(http|https)"/.match(env['CF-VISITOR'])
-        new_env["HTTPS"] = true and new_env["rack.url_scheme"] = "https" and new_env["SERVER_PORT"] = 443 if (match && match[1] == "https")
-        new_env["HTTPS"] = false and new_env["rack.url_scheme"] = "http" and new_env["SERVER_PORT"] = 80 if (match && match[1] == "http")
-      end
-
-      if env["X-FORWARDED-PROTO"]
-        new_env["HTTPS"] = true and new_env["rack.url_scheme"] = "https" and new_env["SERVER_PORT"] = 443 if env["X-FORWARDED-PROTO"].split(',')[0] == "https"
-        new_env["HTTPS"] = false and new_env["rack.url_scheme"] = "http" and new_env["SERVER_PORT"] = 80 if env["X-FORWARDED-PROTO"].split(',')[0] == "http"
-      end
-
-      if @options[:protocol]
-        new_env["HTTPS"] = true and new_env["rack.url_scheme"] = "https" and new_env["SERVER_PORT"] = 443 if @options[:protocol] == "https"
-        new_env["HTTPS"] = false and new_env["rack.url_scheme"] = "http" and new_env["SERVER_PORT"] = 80 if @options[:protocol] == "http"
-      end
-
-      url = Rack::Request.new(new_env).url
+      request_obj = Rack::Request.new(env)
+      url = "#{request_obj.scheme}://#{request_obj.host}#{request_obj.fullpath}"
       prerender_url = get_prerender_service_url()
       forward_slash = prerender_url[-1, 1] == '/' ? '' : '/'
       "#{prerender_url}#{forward_slash}#{url}"
     end
 
-
     def get_prerender_service_url
       @options[:prerender_service_url] || ENV['PRERENDER_SERVICE_URL'] || 'http://service.prerender.io/'
     end