Escape under \x40 control chars in branch name

In this p-r, drone escape branch name in url context.
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We want use under \x40 control chars in branch name but drone does not escape branch name in url context.

Of cause I know under \x40 chars are illegal in branch name. (`git check-ref-format --help`)
We use redmine as bts with github as code repository, so our branch names contain redmine's ticket id:

* `feature/some_fix_#12345`

Please merge this.