upgrade boilerplate packages

ember-app-boilerplate/package.json

@@ -29,10 +29,10 @@
     "@types/ember": "^3.16.2",
     "@types/ember-data": "^3.16.7",
     "@types/ember-qunit": "^3.4.13",
-    "@types/ember__test-helpers": "^1.7.3",
+    "@types/ember__test-helpers": "^2.0.0",
     "@types/qunit": "^2.11.1",
     "@types/rsvp": "^4.0.3",
-    "@typescript-eslint/parser": "4.15.2",
+    "@typescript-eslint/parser": "4.21.0",
     "ember-test-selectors": "^5.0.0",
     "typescript": "^4.1.3"
   },
@@ -44,11 +44,11 @@
     "@glimmer/tracking": "^1.0.3",
     "memserver": "^2.3.7",
     "ember-cli-fastboot": "^2.2.3",
-    "ember-data": "3.25.0",
+    "ember-data": "3.26.0",
     "ember-load-initializers": "^2.1.2",
     "ember-modifier": "^2.1.1",
     "fastboot": "^3.1.2",
-    "mber-head": "^0.1.2",
+    "mber-head": "^0.1.4",
     "node-fetch": "2.6.1"
   },
   "volta": {

ember-app-boilerplate/src/ui/components/welcome-page/template.hbs

@@ -1,4 +1,4 @@
-<div id="ember-welcome-page-id-selector" data-ember-version="{{emberVersion}}">
+<div id="ember-welcome-page-id-selector" data-ember-version="{{this.emberVersion}}">
   <div class="columns">
     <div class="tomster">
       <img src="/images/construction.png" alt="Under construction">
@@ -9,11 +9,11 @@
       <p>You&rsquo;ve officially spun up your very first Ember app :-)</p>
       <p>You&rsquo;ve got one more decision to make: what do you want to do next? We&rsquo;d suggest one of the following to help you get going:</p>
       <ol>
-        <li><a href="https://guides.emberjs.com/v{{emberVersion}}/getting-started/quick-start/">Quick Start</a> - a quick introduction to how Ember works. Learn about defining your first route, writing a UI component and deploying your application.</li>
-        <li><a href="https://guides.emberjs.com/v{{emberVersion}}/tutorial/ember-cli/">Ember Guides</a> - this is our more thorough, hands-on intro to Ember. Your crash course in Ember philosophy, background and some in-depth discussion of how things work (and why they work the way they do).</li>
+        <li><a href="https://guides.emberjs.com/v{{this.emberVersion}}/getting-started/quick-start/">Quick Start</a> - a quick introduction to how Ember works. Learn about defining your first route, writing a UI component and deploying your application.</li>
+        <li><a href="https://guides.emberjs.com/v{{this.emberVersion}}/tutorial/ember-cli/">Ember Guides</a> - this is our more thorough, hands-on intro to Ember. Your crash course in Ember philosophy, background and some in-depth discussion of how things work (and why they work the way they do).</li>
       </ol>
       <p>If you run into problems, you can check <a href="http://stackoverflow.com/questions/tagged/ember.js">Stack Overflow</a> or <a href="http://discuss.emberjs.com/">our forums</a>  for ideas and answers—someone&rsquo;s probably been through the same thing and already posted an answer.  If not, you can post your <strong>own</strong> question. People love to help new Ember developers get started, and our <a href="https://emberjs.com/community/">Ember Community</a> is incredibly supportive.</p>
     </div>
   </div>
-    <p class="postscript">To remove this welcome message, remove the <code>\{{welcome-page}}</code> component from your <code>application.hbs</code> file.<br>You'll see this page update soon after!</p>
+    <p class="postscript">To remove this welcome message, remove the <code>\{{this.welcome-page}}</code> component from your <code>application.hbs</code> file.<br>You'll see this page update soon after!</p>
 </div>