Improve calloc() correctness

[It doesn't _actually_ matter, but technically
the order argument is: (number of items, size of items)]

Closes #279

hiredis.c

@@ -559,7 +559,7 @@ static int processItem(redisReader *r) {
 redisReader *redisReaderCreate(void) {
     redisReader *r;
 
-    r = calloc(sizeof(redisReader),1);
+    r = calloc(1,sizeof(redisReader));
     if (r == NULL)
         return NULL;