patch 8.2.0554: the GUI doesn't set t_Co

Problem:    The GUI doesn't set t_Co.
Solution:   In the GUI set t_Co to 256 * 256 * 256. (closes #5903)
diff --git a/src/version.c b/src/version.c
index a9cdd6a..08a95a5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    554,
+/**/
     553,
 /**/
     552,