patch 8.0.1777: cannot cleanup before loading another colorscheme

Problem:    Cannot cleanup before loading another colorscheme.
Solution:   Add the ColorSchemePre autocommand event.
diff --git a/src/version.c b/src/version.c
index 9881dae..d6be02f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1777,
+/**/
     1776,
 /**/
     1775,