the-farm: fix go-staticcheck warning

[Elfayer]

Task2 asks for:

// negativeFiveFodder says there are -5.0 fodder
fodder, err := DivideFood(negativeFiveFodder, 10)
// fodder == 0.0
// err.Error() == "Negative fodder"

When I type return 0, errors.New("Negative fodder"), VSCode warns out: error strings should not be capitalized (ST1005) go-staticcheck
Same for Task3.

[github-actions]

Dear Elfayer

Thank you for contributing to the Go track on Exercism! 💙
You will see some automated feedback below 🤖. It would be great if you can make sure your PR covers those points. This will save your reviewer some time and your change can be merged quicker.

• 🧦 If you changed the function signature or the function comment in the exemplar file or the stub file (<exercise>.go), make sure the change is applied to both files.

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• 🔤 If your PR fixes an easy to identify typo, if would be great if you could check for that typo in the whole repo. For example, if you found Unicdoe, use "replace all" in your editor (or command line magic) to fix it consistently.

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_{Automated comment created by PR Commenter 🤖.}

[andrerfcsantos]

Thanks for this!