docs(eslint-plugin): fix examples of default-param-last rule

[susisu]

ref: #1407 #1418

The following code is a correct example.

function f(a: number, b = 0, c?: number) {}

[typescript-eslint]

Thanks for the PR, @susisu!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[armano2]

LGTM