cue: add '-local cuelang.org/go' flag for buildins.go

Same as CL 4501, formats buildins.go file with -local flag.

Change-Id: I089d57fe87787a5060c57118d4b48ee365129475
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/4642
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/cue/builtin.go b/cue/builtin.go
index cb3bb8e..4b4a3c5 100644
--- a/cue/builtin.go
+++ b/cue/builtin.go
@@ -13,7 +13,7 @@
 // limitations under the License.
 
 //go:generate go run gen.go
-//go:generate goimports -w builtins.go
+//go:generate goimports -w -local cuelang.org/go builtins.go
 
 package cue