cmd/cue/cmd: make error messages identical on Windows

Fixes build breakage.

Closes #334
https://github.com/cuelang/cue/pull/334

GitOrigin-RevId: 6b72b08debd7bf7db1e204cc40e7aeb9dc9da6df
Change-Id: Id7fcfa2efc6e9993b1a4f962b2ee43b85ddfe008
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/5500
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>
diff --git a/cmd/cue/cmd/import.go b/cmd/cue/cmd/import.go
index 5a0c460..06e07fe 100644
--- a/cmd/cue/cmd/import.go
+++ b/cmd/cue/cmd/import.go
@@ -421,7 +421,8 @@
 				if root != "" {
 					cueFile, _ = filepath.Rel(root, cueFile)
 				}
-				fmt.Fprintf(stderr, "Skipping file %q: already exists.\n", cueFile)
+				fmt.Fprintf(stderr, "Skipping file %q: already exists.\n",
+					filepath.ToSlash(cueFile))
 				if strings.HasPrefix(cueFile, "cue.mod") {
 					fmt.Fprintln(stderr, "Use -Rf to override.")
 				} else {