getCountry() {
		const { digits } = this.state
		// Return `undefined` if no digits have been input yet.
		if (digits) {
			return this._getCountry()
		}
	}
Returns a two-letter country code of the phone number.
Returns `undefined` for "non-geographic" phone numbering plans.
Returns `undefined` if no phone number has been input yet.
@return {string} [country]