docs: remove unneeded whitespace from start of code blocks

[jbampton]

Motivation / Background

This Pull Request standardizes the Markdown code blocks.

Saw we now have a markdown linter so this pr fixes markdown

Detail

Additional information

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[jonathanhefner]

This file is not part of the docs; it is a fixture for the rail_inspector tests. Specifically, it is a snapshot of railties/CHANGELOG.md at 06e9fbd. As such, I don't think it should be changed.

[fatkodima]

Yeah. Since it is already merged, I think this will still work as a fixture?