patch 8.0.1533: libterm doesn't support requesting fg and bg color

Problem:    Libterm doesn't support requesting fg and bg color.
Solution:   Implement t_RF and t_RB.
diff --git a/src/version.c b/src/version.c
index c2096c7..95e5a72 100644
--- a/src/version.c
+++ b/src/version.c
@@ -779,6 +779,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1533,
+/**/
     1532,
 /**/
     1531,