Update dependencies

[connyduck]

Checklist

• Code follows coding conventions held in this repo
• Automated tests have been added
• Tests are passing
• Docs have been updated (if applicable)
• Temporary settings (e.g. variables used during development and testing) have been reverted to defaults

[Simply007]

Hello @connyduck,

sorry for the delay. Took a while until I caught up after Christmas break.

I need to check that Java 8+ is still supported. Did you have any particular reason for the update?

[connyduck]

No particular reason, just noticed when upgrading my own dependencies that yours are out of date as well

[Simply007]

@connyduck, I must apologize. I have completely forgotten about this pull request😞

I have checked the pull requests and it looks OK.

For later reference why 'com.google.guava:guava:23.0 changed to com.google.guava:guava:24.1-jre because they changed version conventions: https://github.com/google/guava/releases/tag/v23.1