Fix ember-canary related issue

Ember.DefaultResolver is no more, so rather trying to use it, we will
simply rely on the basic resolver protocol. That way, not concrete
object is needed, and we are future proof until such time as that
changes.

README.md

@@ -3,7 +3,6 @@
 
 A test-framework-agnostic set of helpers for testing Ember.js applications
 
-
 Compatibility
 ------------------------------------------------------------------------------
 

tests/helpers/resolver.js

@@ -1,5 +1,3 @@
-import Ember from 'ember';
-import { dasherize } from '@ember/string';
 import { assign } from '@ember/polyfills';
 import { setRegistry } from '../../resolver';
 import { setResolver, setApplication } from '@ember/test-helpers';
@@ -40,6 +38,5 @@ export function createCustomResolver(registry) {
     resolve(fullName) {
       return this.registry[fullName];
     },
-
-  }
+  };
 }