docs: Fix typo in Text Styles example

[ajitsonlion]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes
  /start features)

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Needless curly brackets {h1}

What is the new behavior?

• Typo fix

Does this introduce a breaking change?

• Yes
• No

Other information

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