chore(highlight-spec): use this context

Author: gabrielhase

spec/highlighting.spec.js

@@ -425,10 +425,10 @@ Make The <br> W<span class="highlight-spellcheck" data-word-id="spellcheckId" da
     })
 
     it('normalizes a simple text node after removing a highlight', function () {
-      setupHighlightEnv(self, 'People Make The World Go Round')
-      self.highlightRange('myId', 3, 7)
-      const normalizeSpy = sinon.spy(self.div, 'normalize')
-      self.removeHighlight('myId')
+      setupHighlightEnv(this, 'People Make The World Go Round')
+      this.highlightRange('myId', 3, 7)
+      const normalizeSpy = sinon.spy(this.div, 'normalize')
+      this.removeHighlight('myId')
       // There is no way to see the actual error in a test since it only happens in (non-headless)
       // Chome environments. We just check if the normalize method has been called here.
       expect(normalizeSpy.callCount).toEqual(1)