Ensure massdns output is lower case

For some reason some server output part of their response as upper case.
This fails the reading process as it's designed to only work on lower
case for performance reasons.

feed_dns.py

@@ -184,8 +184,8 @@ class MassDnsParser(Parser):
                         select,
                         write,
                         timestamp,
-                        split[0][:name_offset],
+                        split[0][:name_offset].lower(),
-                        split[2][:value_offset],
+                        split[2][:value_offset].lower(),
                     )
                     self.register(record)
                     self.prof.enter_step('parse_massdns')