@desc Updates name servers entry for given domain.

@param {Object} [state] Current state.
@param {string} [domainName] Domain name.
@param {Object} [data] Domain name servers data.
@return {Object} New state
function updateState( state, domainName, data ) {
	const command = {
		[ domainName ]: {
			$set: Object.assign( {}, state[ domainName ] || initialDomainState, data ),
		},
	};

	return update( state, command );
}