cmd/cue: fix up fmt_multi comparison

I suspect that out/star-cue was meant to be a check for star.cue,
not x.cue, which already had out/x.cue.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Iefa68fae3bea616f53ce0639b2f090ff6c44f0d6
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/557333
Reviewed-by: Paul Jolly <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mvdan

cmd/cue/cmd/testdata/script/fmt_multi.txtar

@@ -1,6 +1,6 @@
 exec cue fmt .
 cmp x.cue out/x.cue
-cmp x.cue out/star-cue
+cmp star.cue out/star-cue
 cmp y.cue out/y-cue
 cmp yb.cue out/yb-cue
 -- x.cue --
@@ -45,11 +45,7 @@ package x
 a:  1
 bb: 2
 -- out/star-cue --
-// header
-
-package x
-
-// file comment
+package _
 
 a:  1
 bb: 2