patch 8.0.1809: various typos

Problem:    Various typos.
Solution:   Correct the mistakes, change "cursur" to "cursor". (closes #2887)
diff --git a/src/screen.c b/src/screen.c
index cff6ae5..cac5a3a 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -906,7 +906,7 @@
  * Check if the cursor line needs to be redrawn because of 'concealcursor'.
  */
     void
-conceal_check_cursur_line(void)
+conceal_check_cursor_line(void)
 {
     if (curwin->w_p_cole > 0 && conceal_cursor_line(curwin))
     {