enhance(ci): Test on node 8 and the lastest stable release
enhance(ci): Test on node 8 and the lastest stable release

Because yarn no longer supports node 7:

  warning You are using Node "7.10.1" which is not supported and may encounter bugs or unexpected behavior. Yarn supports the following semver range: "^4.8.0 || ^5.7.0 || ^6.2.2 || >=8.0.0"

LN-Zap/zap-desktop,LN-Zap/zap-desktop,LN-Zap/zap-desktop