patch 8.1.0585: undo test may fail on MS-Windows

Problem:    Undo test may fail on MS-Windows.
Solution:   Also handle lower case drive letters.
diff --git a/src/version.c b/src/version.c
index a25f262..2c8b3ac 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    585,
+/**/
     584,
 /**/
     583,