remove extra "to" from doc comment (#634)

fsnotify.go

@@ -301,7 +301,7 @@ func NewBufferedWatcher(sz uint) (*Watcher, error) {
 //
 // Watching individual files (rather than directories) is generally not
 // recommended as many programs (especially editors) update files atomically: it
-// will write to a temporary file which is then moved to to destination,
+// will write to a temporary file which is then moved to destination,
 // overwriting the original (or some variant thereof). The watcher on the
 // original file is now lost, as that no longer exists.
 //