Fixed bool form signature of several callback methods

[mlpack-bot[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
• Documentation added for any new functionality
• Tests added for any new functionality
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• HISTORY.md updated if the changes are big or user-facing
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Thank you again for your contributions! :+1:

[zoq]

@mlpack-jenkins test this please

[DiscreteLogarithm]

Thank you for your great software :)

[rcurtin]

Thanks! I pushed a changelog entry to HISTORY.md. If you want to add your name to COPYRIGHT.txt please do feel free :smile: 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.