Updated Node.js minimum version required to 8.3.0 (#464)
Updated Node.js minimum version required to 8.3.0 (#464)

Updated Node.js Minimum version required from 7.6 to 8.3.0.
The is because Probot now uses object rest/spread properties, e.g., the rest spread operator: `{ foo, bar, ..., rest } = myObject`
This is available in version 8.3.0 (ES2018). See: [NodeJS ES2018 object rest/spread properties](http://node.green/#ES2018-features-object-rest-spread-properties)
bkeepers/PRobot,probot/probot,probot/probot,probot/probot,bkeepers/PRobot