Minor change (one type hint)

sru/almasru.py

@@ -136,7 +136,7 @@ class RecordRetriever:
         return sru_url
 
     @staticmethod
-    def _response_to_xml(url):
+    def _response_to_xml(url: str) -> Element:
 
         response = request.urlopen(url).read()
         xml = fromstring(response)