Fix ruby-head support

Author: byroot

lib/global_id/uri/gid.rb

@@ -173,5 +173,9 @@ def parse_query_params(query)
       end
   end
 
-  @@schemes['GID'] = GID
+  if respond_to?(:register_scheme)
+    register_scheme('GID', GID)
+  else
+    @@schemes['GID'] = GID
+  end
 end