Fix stupid typo in lookup_tag()

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>

tag.c

@@ -30,7 +30,7 @@ struct tag *lookup_tag(const unsigned char *sha1)
 	if (!obj->type)
 		obj->type = OBJ_TAG;
         if (obj->type != OBJ_TAG) {
-                error("Object %s is a %s, not a tree",
+                error("Object %s is a %s, not a tag",
                       sha1_to_hex(sha1), typename(obj->type));
                 return NULL;
         }