Wrap ssh cmd in quotes

This prevents the accidental execution of commands on the local machine.

I have noticed that in

    deploy:
        ssh:
            [...]
            cmd: cd public_html && tar xvf pub_2014_wac.tar.gz

the second part of `cmd` seems to be executed in the container instead of on the remote. This is due to bash interpreting `&&` as not part of the argument for `ssh` but as an operator for itself. Wrapping the entire `ssh` command in quotes helps.

Secondly, I think it would make more sense to have a list of commands similar to the `script` section of `.drone.yml`.