upgrade ember cli to 3.8 LTS

[EndangeredMassa]

I used ember-cli-update (and manual changes) to upgrade this repo to ember-cli 3.4, which is the most recent LTS release.

The test suite still passes locally and I manually linked this to a local app, which also still worked.

We still need to:

• make it clear which versions of this addon work with which versions of Ember
• update the documentation examples to use modern async testing syntax Update to new async syntax #95 / add async/await syntax to readme (closes #95) #96

[rwjblue]

Sorry about the delays here @EndangeredMassa. I did a quick pass after reviewing the CI failures with some inline suggestions. There is one that will require a bit more hand tweaking on your end (the "in a jQuery context" test), but I tried to explain what needed to change.

I think that with these changes, CI should pass...

[MelSumner]

@EndangeredMassa I updated to 3.8 which is now latest LTS

[MelSumner]

after merging this, we'll need to do a major version bump.

[MelSumner]

I updated this branch so it uses 3.8 LTS instead of 3.4, updated ember-try and travis config, and added the jQuery check that @rwjblue suggested. Thank you for working on this, @EndangeredMassa !

[MelSumner]

@rwjblue do you think this is okay to merge now?

[drewlee]

These changes are preventing #123 from moving forward. I don't have full context, but @MelSumner, @EndangeredMassa, is this stable to merge with the main branch?

[SergeAstapov]

@MelSumner @EndangeredMassa @drewlee created #138 with upgrade to 3.12. Happy to help push it over the line