patch 8.0.0286: not always redrawing after screen resize

Problem:    When concealing is active and the screen is resized in the GUI it
            is not immediately redrawn.
Solution:   Use update_prepare() and update_finish() from
            update_single_line().
diff --git a/src/version.c b/src/version.c
index e47b0d3..4a3c971 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    286,
+/**/
     285,
 /**/
     284,