Unhandled promise rejection

[mshing]

When running tests in parallel using chrome headless browser I get intermittent failures on random tests with the following error using node v8.9.4 and would prevent the process from completing.

 e2e/design-tokens   ✔ Element <.vrt-frame> was visible after 79 milliseconds. 
 e2e/design-tokens   ERROR: Unable to locate element: ".vrt-frame" using: css selector
 e2e/design-tokens       at new Promise (<anonymous>)
 e2e/design-tokens   ✖ The screenshot for selector <.vrt-frame> could not be captured.
 e2e/design-tokens       at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)
 e2e/design-tokens   img1 and img2 must be an Jimp images
 e2e/design-tokens   (node:93742) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): undefined
 e2e/design-tokens   (node:93742) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

I managed to get around this by setting retries for nightwatch and adding a catch to the promise created in lib/compare-with-baseline.js.