patch 8.1.0767: when deleting lines at the bottom signs are misplaced

Problem:    When deleting lines at the bottom signs are misplaced.
Solution:   Properly update the line number of signs at the end of a buffer
            after a delete/undo operation. (Yegappan Lakshmanan, closes #3798)

src/version.c

@@ -791,6 +791,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    767,
 /**/
     766,
 /**/