Change Content-type to Content-Type (#4481)

Co-authored-by: santosh <santosh@acalvio.com>

scrapy/responsetypes.py

@@ -71,7 +71,7 @@ class ResponseTypes:
         cls = Response
         if b'Content-Type' in headers:
             cls = self.from_content_type(
-                content_type=headers[b'Content-type'],
+                content_type=headers[b'Content-Type'],
                 content_encoding=headers.get(b'Content-Encoding')
             )
         if cls is Response and b'Content-Disposition' in headers: