[mutter] Update POTFILES.in

[Piotr Drąg <piotrdrag src gnome org>]

commit 5480a3f23848a41b9de4a3569f08f1c1f71edd63
Author: Piotr Drąg <piotrdrag gmail com>
Date:   Fri May 3 12:54:24 2019 +0200

    Update POTFILES.in

 po/POTFILES.in | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/po/POTFILES.in b/po/POTFILES.in
index ec3c66257..028d7e278 100644
--- a/po/POTFILES.in
+++ b/po/POTFILES.in
@@ -26,6 +26,7 @@ src/ui/theme.c
 src/wayland/meta-wayland-tablet-pad.c
 src/x11/meta-x11-display.c
 src/x11/meta-x11-errors.c
+src/x11/meta-x11-selection-input-stream.c
 src/x11/session.c
 src/x11/window-props.c
 src/x11/xprops.c