2020 Hacktoberfest special

Many thanks to @cah-danmonroe, @esbanarango, and @takshch for helping out with the Hacktoberfest issues!

In the patch release, you will find 4 internal changes:

• Added demoURL to package.json (to display the link in Ember Observer)
• Added ember-lts-3.20 to ember-try test matrix
• Used ember-truth-helpers instead of custom helpers for the demo app
• Upgraded ember-source to v3.22.0 and ember-cli-babel to v7.23.0

The risk in upgrading ember-container-query from v1.1.4 to v1.1.5 should be between none and small.