docs(guide/Components): snake -> kebab

[knpwrs]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Doc correction.

What is the current behavior? (You can also link to an open issue here)

Docs mention snake_case.

What is the new behavior (if this is a feature change)?

Example given is actually kebab-case.

Does this PR introduce a breaking change?

No.

Please check if the PR fulfills these requirements

• 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)

Other information:

The example given is not in snake_case, it is in kebab-case.

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[knpwrs]

I signed it!

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