Use HEAD instead of master as current

[leny]

Hi,

Got into a small issue when using this action within a repo with no master branch (or with a default branch not called master), due to the following line:

git push --force $REMOTE_REPO master:$REMOTE_BRANCH

By using HEAD instead of directly mention master, we can fix this.

[maxheld83]

yeah, thanks @leny that makes a ton more sense.
If people want to only deploy from master (or whatever), they should use a filter action before.
This action should just deploy from whatever branch happens to be in github/workspace at the time.