Update nightwatch to v2

[MMMalik]

Are you reporting a feature request or a bug?

Task

Expected result

• Nightwatch is updated to v2.
• Running npm audit does not report any security vulnerabilities related to nightwatch.

Actual result

There are several vulnerabilities of moderate severity reported by npm audit. They are related to packages that nightwatch depends on.

Other details

As per https://github.com/nightwatchjs/nightwatch/pull/2908, these issues will be resolved in nightwatch@2. Let's wait until a stable version of nightwatch@2 is released and use it in ckeditor4-react project.

[MMMalik]

Completed as part of https://github.com/ckeditor/ckeditor4-react/pull/275.

No additional actions were required on our side.