rename onError to onFail for consistency

[kiftio]

What changes are you making?

Optional change, opening for awareness of the inconsistency.

    @discardableResult public func onFail(_ action: @escaping (CheckoutError) -> Void) -> Self {
        delegate.onFail = action
        return self
    }

    override fun onFail(error: CheckoutException) {

I tested by adding in a throw when opening the sheets from the native side, and seeing that they propagate to the react native handler in the js debugger:

ios

android

PR Checklist

Important

• I've added tests to support my implementation
• I have read and agree with the Contribution Guidelines.
• I have read and agree with the Code of Conduct.
• I've updated the README.

Releasing a new version of the kit?

• I have bumped the version number in the package.json file.

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[github-actions]

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