[slack] No branch or commit name about recipes

[pedroresende]

@andrey-helldar found a work around for this.

In your deploy.php file, add the following

set('revision', function() {
    return runLocally('git rev-parse HEAD');
});
set('slack_text', 'Deploying `{{revision}}` to *{{stage}}*');

for the case of the tag,

set('tag', function() {
    return runLocally('git describe --tags');
});
set('slack_text', 'Deploying `{{tag}}` to *{{stage}}*');

[pedroresende]

exactly the same problem with --tag