Fix css specifity bug with favorite icon

[yavorski]

If i change the first item in api/posts.json to this, where the actual change is "favorite": true, the favorite icon stays the same (not changing to red) until you hover it.

{
  "uid": 1,
  "text" : "Have you heard about the Web Components revolution?",
  "username" : "Eric",
  "avatar" : "../images/avatar-01.svg",
  "favorite": true
}

Seems this selector is not working in the beginning until you hover the icon:

:host([favorite]) core-icon-button {
  color: #da4336;
}

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[yavorski]

@googlebot done :)