Refactor Hero example

[Abhishek01039]

Update the code sample of the hero widget

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

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[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

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[Abhishek01039]

Hello @goderbauer @Piinks
can anyone please review this PR?
Thanks

[goderbauer]

LGTM

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

• The status or check suite Linux flutter_plugins has failed. Please fix the issues identified (or deflake) before re-applying this label.