Fixed bool form signature of several callback methods

[DiscreteLogarithm]

No description provided.

[mlpack-bot]

Thanks for opening your first pull request in this repository! Someone will review it when they have a chance. In the mean time, please be sure that you've handled the following things, to make the review process quicker and easier:

• All code should follow the style guide
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[zoq]

@mlpack-jenkins test this please

[zoq]

Thanks for the patch.

[DiscreteLogarithm]

Thank you for your great software :)

[mlpack-bot]

Second approval provided automatically after 24 hours. 👍

[rcurtin]

Thanks! I pushed a changelog entry to HISTORY.md. If you want to add your name to COPYRIGHT.txt please do feel free 😄 I want to make a follow-up PR to update documentation in a couple places, I'll do that shortly.

[DiscreteLogarithm]

Thank you as well.

If you want to add your name to COPYRIGHT.txt please do feel free 😄

No it's fine.

[zoq]

Thanks again for the contribution.