docs(RootRouter): describe your change...

[jwcarroll]

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

Documentation update

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

Simple typo

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

Fixed typo

Does this PR introduce a breaking change?

Nope

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:

Simple typo fix from betweent he to between the

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[jwcarroll]

I signed it!

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[googlebot]

CLAs look good, thanks!