Enable electron-builder debugging on travis to ensure that output is
produced whilst long running electron (re)build steps are running. This
can prevent build timeouts.
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"