add missing tokenRegex argument

[fabianmieller]

No description provided.

[ljharb]

this was intentionally not provided - see #64 (comment)

[fabianmieller]

@ljharb
I'm using a custom interpolations and when the onMissingKey case happens i want to use the Polyglot.transformPhrase function with the tokenRegEx parameter. Currently this is not possible and the default token regex is used and i can't pass the customized interpolation regex.

const polyglot = new Polyglot({

    interpolation: {
        prefix: '%',
        suffix: '%',
    }

    onMissingKey(key, interpolations, locale, tokenRegEx) {

        // ....

        return Polyglot.transformPhrase(key, interpolations, locale, tokenRegEx);
    }

});