Add deploy command for Sprint.ly

Adds a command to mark items as deployed with [Sprint.ly's Deploys API](https://sprintly.uservoice.com/knowledgebase/articles/138392-deploys). 

> sprintly 1234 production deploy 42,43

Also allows you to store the default environment to which you typically deploy.

> sprintly default_env production

Fixed this warning: `WARNING @http() is going to be deprecated in 3.0.0 use @robot.http()`