Allow user to change status manually

[ngs]

Hi,

This change allows user to

• retrieve deployment ID from print output
• manually update deployment status

with configuration

# config/deploy.rb
set :current_github_deployment, ENV['GITHUB_DEPLOYMENT']

retrieve ID from listing

$ cap production github:deployments

Deployment#12345 (unknown): 2017-03-16 19:26:25 UTC master@abc... to production by @ngs

then run

$ GITHUB_DEPLOYMENT=12345 cap production github:deployment:error

[mikz]

Good change! Thank you.

I'd be a bit worried about discoverability of this feature. Do you mind adding it to the README ?

And I'd consider changing the variable from current_github_deployment to existing_github_deployment to imply it is not going to be created but already has to exist.