artstation: fix fetch source data for image urls.

Fixes 'Fetch source data' when uploading an image url and the referer
url is available:

* https://danbooru.donmai.us/uploads/new?url=https://cdna.artstation.com/p/assets/images/images/006/029/978/large/amama-l-z.jpg&ref=https://www.artstation.com/artwork/4BWW2

app/logical/sources/site.rb

@@ -14,12 +14,12 @@ module Sources
       [Strategies::PixivWhitecube, Strategies::Pixiv, Strategies::NicoSeiga, Strategies::DeviantArt, Strategies::ArtStation, Strategies::Nijie, Strategies::Twitter, Strategies::Tumblr, Strategies::Pawoo]
     end
 
-    def initialize(url, options = {})
+    def initialize(url, referer_url: nil)
       @url = url
 
       Site.strategies.each do |strategy|
-        if strategy.url_match?(url)
-          @strategy = strategy.new(url, options[:referer_url])
+        if strategy.url_match?(url) || strategy.url_match?(referer_url)
+          @strategy = strategy.new(url, referer_url)
           break
         end
       end