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.

src/testdir/test_undo.vim

@@ -426,7 +426,7 @@ funct Test_undofile()
   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')

src/version.c

@@ -799,6 +799,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    585,
 /**/
     584,
 /**/