node--content-type.tpl.php did not override and now i stuck in using node override with content type.
I followed these step.


Create new content type name post (machine name: post)
Copy node.tpl.php from module to
my_theme/templates/node/node--post.tpl.php
Go to admin-configuration-performance and click "Clear all caches"


Well, it did not work.

Sorry for create duplicated article, but when i followed from answer, it did not work too.
If you created your sub theme correctly, the sub theme is located under drupal/sites/all/themes/ and NOT in the drupal/themes folder.

So your tpl.php file needs to be in 


  drupal/sites/all/themes/commons_child/templates