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/testdir/test_undo.vim b/src/testdir/test_undo.vim
index e06abff..7c93e23 100644
--- a/src/testdir/test_undo.vim
+++ b/src/testdir/test_undo.vim
@@ -426,7 +426,7 @@
   let cwd = getcwd()
   if has('win32')
     " Replace windows drive such as C:... into C%...
-    let cwd = substitute(cwd, '^\([A-Z]\):', '\1%', 'g')
+    let cwd = substitute(cwd, '^\([a-zA-Z]\):', '\1%', 'g')
   endif
   let cwd = substitute(cwd . '/Xundofoo', '/', '%', 'g')
   if has('persistent_undo')
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,