Fix helper name in docs

docs/app/templates/public-pages/docs/migrate-7-0-to-8-0.hbs

@@ -22,7 +22,7 @@
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-    <p>Helper: The helper <code>power-select-is-selected</code> was renamed to <code>ember-power-select-is-equal</code>. If you have used in your custom components, you need to replace it</p>
+    <p>Helper: The helper <code>ember-power-select-is-selected</code> was renamed to <code>ember-power-select-is-equal</code>. If you have used in your custom components, you need to replace it</p>
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     <p>Vanilla JS: If you have used vanilla js you must now import the css in <code>app.js</code> manually like (for other css adding examples see under installation)</p>