server: bump protocol version

We have new options added.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/server.h b/server.h
index adb190a..85d9d7e 100644
--- a/server.h
+++ b/server.h
@@ -38,7 +38,7 @@
 };
 
 enum {
-	FIO_SERVER_VER			= 30,
+	FIO_SERVER_VER			= 31,
 
 	FIO_SERVER_MAX_FRAGMENT_PDU	= 1024,