Fix config watch (#1670)

* add dirty overrite test case

* need version to figure out if config need update or not

* using nanosecond as version for two goroutine can run in same second

* config should check snapshot version when update

* set checksum of ChangeSet

Co-authored-by: Asim Aslam <asim@aslam.me>

config/source/memory/memory.go

@@ -42,6 +42,7 @@ func (s *memory) Watch() (source.Watcher, error) {
 }
 
 func (m *memory) Write(cs *source.ChangeSet) error {
+	m.Update(cs)
 	return nil
 }