Add ember-tether to dependencies

[barryofguilder]

This adds ember-tether to the package "depencencies" and will fix #1484.

[barryofguilder]

Hmm, with pnpm, I still get the following error unless the consuming test-app specifies ember-tether in it's dependencies. I'm not great with dependency resolution, so not sure what needs to be changed.

Edit: Should it be changed to be a peer dependency?

[RobbieTheWagner]

@barryofguilder thanks for the PR! I think what you have here is correct because ember-tether is a peerDep of ember-modal-dialog. Let's try merging and releasing this and see if the released version works for you.

[barryofguilder]

@barryofguilder thanks for the PR! I think what you have here is correct because ember-tether is a peerDep of ember-modal-dialog. Let's try merging and releasing this and see if the released version works for you.

Yep, after installing this version, I was able to remove ember-tether from my test-app and it still worked.