fix casing in import statement

[XenoPhex]

This library is causing us to have two folders in our vendor called Sirupsen and sirupsen. According to the sirupsen/logrus's README:

Everything using logrus will need to use the lower-case: github.com/sirupsen/logrus. Any package that isn't, should be changed.

Fixing these import statements would save us some duplication.

[msftclas]

@XenoPhex,
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[lussn]

Thanks @XenoPhex , same issue here.

[XenoPhex]

Adding a link back to the original issue: moby/moby#33641

[msftclas]

@XenoPhex, thanks for signing the contribution license agreement. We will now validate the agreement and then the pull request.

Thanks, Microsoft Pull Request Bot

[XenoPhex]

Legal finally got back to me, got all the things signed!

[jstarks]

Great, thanks!

I'll go ahead and merge this one since this repo doesn't see many modifications. Then moby can revendor whenever they're ready.