Deal with network-path reference redirects

fixes #491

lib/httparty/request.rb

@@ -76,7 +76,13 @@ module HTTParty
         path.path = last_uri_host + path.path
       end
 
-      new_uri = path.relative? ? options[:uri_adapter].parse("#{base_uri}#{path}") : path.clone
+      if path.relative? && path.host
+        new_uri = options[:uri_adapter].parse("#{@last_uri.scheme}:#{path}")
+      elsif path.relative?
+        new_uri = options[:uri_adapter].parse("#{base_uri}#{path}")
+      else
+        new_uri = path.clone
+      end
 
       # avoid double query string on redirects [#12]
       unless redirect

spec/httparty/request_spec.rb

@@ -230,6 +230,14 @@ RSpec.describe HTTParty::Request do
 
         expect(@request.uri).to eq(URI.parse("http://example.com/bar?foo=bar"))
       end
+
+      it "returns correct path when the server sets the location header to a network-path reference" do
+        @request.last_uri = URI.parse("https://example.com")
+        @request.path = URI.parse("//www.example.com")
+        @request.redirect = true
+
+        expect(@request.uri).to eq(URI.parse("https://www.example.com"))
+      end
     end
 
     context "query strings" do