patch 8.1.0566: SGR not enabled for mintty because $TERM is "xterm"

Problem:    SGR not enabled for mintty because $TERM is "xterm".
Solution:   Detect mintty by the termresponse. (Ken Takata, closes #3667)
diff --git a/src/version.c b/src/version.c
index e4f863e..b912a6e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    566,
+/**/
     565,
 /**/
     564,