patch 8.1.0081: the terminal debugger doesn't adjust to changed 'background'

Problem:    The terminal debugger doesn't adjust to changed 'background'.
Solution:   Add an OptionSet autocommand. (Christian Brabandt)
diff --git a/src/version.c b/src/version.c
index ebcc4ef..39b317f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    81,
+/**/
     80,
 /**/
     79,