github delete remote branch/tag

https://help.github.com/articles/pushing-to-a-remote/

delete remote branch

git push  <REMOTENAME> :<BRANCHNAME>

However, here, you're telling Git to push nothing
into BRANCHNAME on REMOTENAME. Because of this, git push deletes the branch
on the remote repository. 

delete remote tag 

https://stackoverflow.com/questions/5480258/how-to-delete-a-git-remote-tag


github的tag一定是 create time，無法push過去的tag