Value: place nocmp zero-sized field first (#109)

value.go

@@ -25,7 +25,7 @@ import "sync/atomic"
 // Value shadows the type of the same name from sync/atomic
 // https://godoc.org/sync/atomic#Value
 type Value struct {
-	atomic.Value
-
 	_ nocmp // disallow non-atomic comparison
+
+	atomic.Value
 }