fix: upgrade ember

.travis.yml

@@ -1,7 +1,7 @@
 ---
 language: node_js
 node_js:
-  - "4"
+  - "8"
 
 sudo: false
 dist: trusty
@@ -10,8 +10,7 @@ addons:
   chrome: stable
 
 cache:
-  directories:
-    - $HOME/.npm
+  yarn: true
 
 env:
   global:
@@ -35,13 +34,15 @@ matrix:
   allow_failures:
     - env: ALLOW_DEPRECATIONS=true EMBER_TRY_SCENARIO=ember-canary
 
+install:
+  - yarn install --no-lockfile --non-interactive
+
 before_install:
-  - npm config set spin false
-  - npm install -g npm@4
-  - npm --version
+  - curl -o- -L https://yarnpkg.com/install.sh | bash
+  - export PATH=$HOME/.yarn/bin:$PATH
 
 script:
-  - npm run lint:js
+  - yarn lint:js
   # Usually, it's ok to finish the test scenario without reverting
   #  to the addon's original dependency state, skipping "cleanup".
   - node_modules/.bin/ember try:one $EMBER_TRY_SCENARIO --skip-cleanup

app/initializers/resize.js

@@ -1,8 +1,6 @@
-import Ember from 'ember';
 import ResizeService from 'ember-resize/services/resize';
 import config from '../config/environment';
-
-const { getWithDefault } = Ember;
+import { getWithDefault } from '@ember/object';
 
 export function initialize() {
   let application = arguments[1] || arguments[0];

config/ember-try.js

@@ -9,6 +9,7 @@ module.exports = function() {
     getChannelURL('canary')
   ]).then((urls) => {
     return {
+      useYarn: true,
       scenarios: [
         {
           name: 'ember-lts-2.12',