ui-snapshot: actually compress zip archives

Since cgit linked with git-1.6.0 all zip archives has been uncompressed.
This patch fixes the issue by specifying Z_DEFAULT_COMPRESSION.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

ui-snapshot.c

@@ -86,6 +86,7 @@ static int make_snapshot(const struct cgit_snapshot_format *format,
 	}
 	args.tree = commit->tree;
 	args.time = commit->date;
+	args.compression_level = Z_DEFAULT_COMPRESSION;
 	ctx.page.mimetype = xstrdup(format->mimetype);
 	ctx.page.filename = xstrdup(filename);
 	cgit_print_http_headers(&ctx);