RESP3: change streams items from maps to arrays.

Streams items are similar to dictionaries, however they preserve both
the order, and allow for duplicated field names. So a map is not a
semantically sounding way to deal with this.

https://twitter.com/antirez/status/1248261087553880069

src/t_stream.c

@@ -963,7 +963,7 @@ size_t streamReplyWithRange(client *c, stream *s, streamID *start, streamID *end
         addReplyArrayLen(c,2);
         addReplyStreamID(c,&id);
 
-        addReplyMapLen(c,numfields);
+        addReplyArrayLen(c,numfields*2);
 
         /* Emit the field-value pairs. */
         while(numfields--) {