Update nightwatch version to use latest

Bump Nightwatch version devDependency to "latest" from "0.4.14"

Status: **Opened for visibility**
Reviewers: @scalvert @marlowpayne @ellenmobify 

## Changes
- Changed nightwatch version to use "latest" from hardcoded value

## Notes
- nightwatch version is really old (0.4.14) updated to use the latest version