pkg/time: fix documentation bug in Unix

returns UTC, not local

Fixes #930

Change-Id: I9baf6495b8c5a5cca33e8842d241c44b2c1c154d
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/9525
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

pkg/time/time.go

@@ -192,7 +192,7 @@ func Parse(layout, value string) (string, error) {
 	return t.UTC().Format(time.RFC3339Nano), nil
 }
 
-// Unix returns the local Time corresponding to the given Unix time,
+// Unix returns the Time, in UTC, corresponding to the given Unix time,
 // sec seconds and nsec nanoseconds since January 1, 1970 UTC.
 // It is valid to pass nsec outside the range [0, 999999999].
 // Not all sec values have a corresponding time value. One such