patch 8.1.0726: redrawing specifically for conceal feature

Problem:    Redrawing specifically for conceal feature.
Solution:   Use generic redrawing methods.
diff --git a/src/normal.c b/src/normal.c
index 9ee0eef..c973fa1 100644
--- a/src/normal.c
+++ b/src/normal.c
@@ -8512,7 +8512,7 @@
 	{
 #ifdef FEAT_CONCEAL
 	    if (curwin->w_p_cole > 0 && oldline != curwin->w_cursor.lnum)
-		update_single_line(curwin, oldline);
+		redrawWinline(curwin, oldline);
 #endif
 	    /* When '#' is in 'cpoptions' ignore the count. */
 	    if (vim_strchr(p_cpo, CPO_HASH) != NULL)