clean useless whitespaces in filter-branch example

[maximd]

Why: the double and trailing whitespaces are not needed in the git filter-branch example

What's being changed: remove the double whitespace and the trailing whitespace

Check off the following:

• All of the tests are passing.
• I have reviewed my changes in staging. (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[welcome]

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[janiceilene]

@maximd Thanks so much for opening a PR! I'll get this triaged for review ⚡

[hubwriter]

@maximd - Good change 👍
Thanks for taking the time to correct this.

[github-actions]

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