patch 8.0.1544: when using 'termguicolors' SpellBad doesn't show

Problem:    When using 'termguicolors' SpellBad doesn't show.
Solution:   When the GUI colors are not set fall back to the cterm colors.
diff --git a/src/version.c b/src/version.c
index 09dcc57..07fc3d6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -779,6 +779,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1544,
+/**/
     1543,
 /**/
     1542,