docs (router): fixes typo on segments

[mkanyar]

PR Checklist

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

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.io application / infrastructure changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

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Does this PR introduce a breaking change?

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• No

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[atscott]

@mkanyar LGTM. Please follow #45411 (comment) to sign the CLA so this can be merged

[mkanyar]

@mkanyar LGTM. Please follow #45411 (comment) to sign the CLA so this can be merged

I already signed it

[dylhunn]

This PR was merged into the repository by commit 85782e6.

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