patch 8.0.0421: diff mode wrong when adding line at end of buffer

Problem:    Diff mode is displayed wrong when adding a line at the end of a
            buffer.
Solution:   Adjust marks in diff mode. (James McCoy, closes #1329)

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    421,
 /**/
     420,
 /**/