docs: Miss double quotation on the db.json

[iamxiaobing47]

The id on the db.json should be with "", otherwise it returns Not Found error Reference: https://www.npmjs.com/package/json-server

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• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/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?

The tutorial-14-http demonstrates how to mock a json-server and provides a db.json file. However, the application cannot connect to http://localhost:3000/locations/{id}, because as mentioned in the doc https://www.npmjs.com/package/json-server, the id should be with double quotes

Issue Number: N/A

What is the new behavior?
The application can connect to http://localhost:3000/locations/{id} now

Does this PR introduce a breaking change?

• Yes
• [x ] No

Other information