async/await e2e and disable selenium promise manager (closes #399)

[captaincaius]

deprecated SELENIUM_PROMISE_MANAGER now set to false so release/6.0 will be a little more future-proof ;)

[sinedied]

Perfect! It might also be useful to add a note on this and a link to https://www.protractortest.org/#/async-await in the e2e test guide 😉

[captaincaius]

Yup you're right - I'll try to add a commit to this PR tonight. Maybe a quick note too saying that older examples you might find on the internet might be missing async/await because they might have had it enabled or something.

[captaincaius]

Hmm... something up w/ the appveyor builds? Seems unrelated to the PR.

[sinedied]

Yes it's strange, maybe related to latest ng-cli update :/
Since travis is OK, we can merge this anyways after you've updated the docs.

[captaincaius]

Perfect! It might also be useful to add a note on this and a link to https://www.protractortest.org/#/async-await in the e2e test guide

Donezo. maybe I got a little carried away with the advertisements to protractor's docs but at least it's super clear :D. LMK if it needs revision.

[sinedied]

That's perfect 😉