docs(guide/Component Router): Add missing backticks

[bubersson]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
docs fix
What is the current behavior? (You can also link to an open issue here)
What is the new behavior (if this is a feature change)?
Does this PR introduce a breaking change?
Please check if the PR fulfills these requirements

• [y] The commit message follows our guidelines: https://github.com/angular/angular.js/blob/master/CONTRIBUTING.md#commit-message-format
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
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[bubersson]

I signed it!

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