Support ember-render-helpers v1

[jelhan]

Ember Leaftlet depends on version 0.2 of ember-render-helpers today. There was recently a v1.0 release of ember-render-helpers. It would be great if ember-leaflet supports it to unblock consumers from upgrading. Especially as many different addons depend on ember-render-helpers.

We cannot even use resolutions to enforce v1.0 for ember-render-helpers. That fails because ember-render-helpers has been upgraded to a v2 addon. But Ember Leaflet does not depend on ember-auto-import@v2 yet.